KARKAMIS - Turkish tanks backed by fighter jets and special forces rolled into Syria Wednesday in an unprecedented operation to drive Islamic State militants out of a key Syrian border town.

The air and ground offensive also involving Syrian fighters - the most ambitious launched by Ankara in the Syria conflict - is aimed at clearing militants from the town of Jarabulus directly opposite Turkey .

But President Recep Tayyip Erdogan emphasised the operation was also targeting Kurdish militia fighters strongly opposed by Ankara - but backed by the US as a key ally against IS - who had also been closing in on Jarabulus.  The operation - named “Euphrates Shield” - began at around 4:00 am (0100 GMT) with Turkish artillery pounding dozens of IS targets around Jarabulus, the Turkish prime minister’s office said. Turkish F-16 fighter jets, backed by US-led coalition war planes, also hit targets inside Syria .

The Syrian government condemned Wednesday’s Turkish incursion into the Islamic State group-held border district of Jarabulus as a “flagrant violation” of its sovereignty. The foreign ministry said it “condemns the crossing of the Turkey-Syria border by Turkish tanks and armoured vehicles towards the town of Jarabulus with air cover from the US-led coalition and considers it a flagrant violation of Syrian sovereignty.

An AFP photographer saw around a dozen Turkish tanks cross into Syria in support of Syrian opposition fighters who had also crossed and 1,500 of whom were now in the area according to state media.

Tensions had flared across the Syria-Turkey border on Tuesday following rocket fire from Jarabulus which landed inside Turkey . Turkish state media said the operation rapidly notched up its first success with the Syrian fighters taking from IS the village of Keklijah five kilometres (three miles) west of Jarabulus. As well as tanks , the AFP photographer in the area of Karkamis opposite Jarabulus saw several smaller military vehicles believed to be carrying the pro-Ankara Syrian rebels. Security sources quoted by Turkish television said a small contingent of special forces had travelled into Syria to secure the area before a possible larger ground operation.

Turkish authorities had late Tuesday ordered the evacuation of Karkamis for safety reasons, raising expectations that an offensive was imminent.

Turkey will want to show with the operation that it is serious about taking on IS, which has been blamed for a string of attacks inside the country, the latest a weekend attack on a Kurdish wedding in Gaziantep that left 54 people dead, many of them children.

Turkish tanks and hundreds of opposition fighters thrust deep inside Syrian territory Wednesday in a lightning operation that within hours ousted Islamic State jihadists from a key Syrian border town.

The air and ground offensive - the most ambitious launched by Ankara in the Syria conflict - made rapid progress towards Jarabulus with rebel fighters already proclaiming victory by the late afternoon just 14 hours after it started.

"Jarabulus is completely liberated," Ahmad Othman, a commander of the Sultan Mourad rebel group, told AFP from the scene, while another rebel spokesman said IS fighters had fled towards Al-Bab to the southwest.

Turkey 's state-run Anadolu news agency said the Syrian fighters had taken the town centre, with just one Syrian rebel fighter killed and 10 wounded. No Turkish forces lost their lives.

Turkish President Recep Tayyip Erdogan emphasised the operation was also targeting Kurdish militia fighters strongly opposed by Ankara - but backed by the US as a key ally against IS - who had also been closing in on Jarabulus.

But visiting US Vice President Joe Biden reassured Turkey that Washington had told the Kurdish fighters under no circumstances to cross west of the Euphrates River or face the total loss of American support.

A dozen Turkish tanks then rolled into Syria along with hundreds of Syrian opposition fighters in pick-ups who then moved south towards Jarabulus.

US A-10s and F-16s warplane also hit IS targets in Syria in support of the offensive , a US official said.

The effects of one air raid on the northern outskirts of Jarabulus were easily visible, sending up a cloud of black smoke and sand.

The speed of the advance was stunning and stood in stark contrast to the long, grinding battles it had taken for Kurdish forces to recapture towns from IS in northern Syria , such as Kobane and Manbij.

Turkey 's NTV television said that IS militants had shown little resistance to the advancing forces. The Dogan news agency said 46 jihadists were killed but this was not confirmed by officials.

Reconnaissance teams of the Syrian fighters were now working in the centre of Jarabulus to check for any explosives left behind by the jihadists.

A Turkish official, who declined to be named, said: "Turkey will continue operations until we are convinced that imminent threats against the country's national security have been neutralised."

Turkey wants to show it is serious about taking on IS, which has been blamed for a string of attacks inside the country - the latest a weekend attack on a Kurdish wedding in Gaziantep that left 54 people dead, many of them children.

Ankara has in the past been accused of turning a blind eye to the rise of IS in Syria and even aiding its movements to-and-fro across the border, claims the government had always vehemently denied.

Turkey has long been alarmed about the activities inside Syria of the People's Protection Units (YPG) militia, which Washington sees as an ally but Ankara regards as a terror group.

But Biden on Wednesday said Washington had made clear to pro-Kurdish forces in Syria that they must not cross west of the Euphrates River.

"They cannot, will not and under no circumstances (will) get American support if they do not keep that commitment. Period," he said.

Saleh Moslem, head of the Democratic Union Party (PYD), the YPG's political wing, tweeted that Turkey was now in the "Syrian quagmire" and would be "defeated" like IS.

But a senior US administration official said Washington had already been "syncing up" with Turkey for the operation and US advisors had been in a planning cell.

Erdogan said the operation was aimed against both IS and PYD - "terror groups that continuously threaten our country in northern Syria ".

However Prime Minister Binali Yildirim acknowledged at the weekend for the first time that Assad was one of the "actors" in Syria and may need to stay on as part of a transition.

But in a note of discord, Russia said it was "deeply concerned" at the situation on the border warning of a "further degeneration of the situation".

Assad's government - which has long has little sway in this region - condemned the incursion as a "flagrant violation" of its sovereignty.

"We have said 'enough is enough'... This now needs to be resolved," he said.

The Turkish air strikes were the first since a November crisis with Russia sparked when the Turkish air force downed one of Moscow's warplanes.

The movements have come at a critical juncture for Turkey in Syria 's five-and-a-half-year war, with signs growing it is on the verge of a landmark policy shift.

Ankara has always called for the removal of President Bashar al-Assad, putting Turkey at odds with his main supporters Iran and Russia.

Biden is likely to face expressions of alarm from Turkey about the activities inside Syria of the People’s Protection Units (YPG) militia, which Washington sees as an ally but Ankara regards as a terror group.

Saleh Moslem, the head of the Democratic Union Party (PYD), the YPG’s political wing, tweeted that Turkey was now in the “Syrian quagmire” and would be “defeated” like IS. But a senior US administration official said Washington had already been “syncing up” with Turkey for the operation and US advisors had been in a planning cell.

Crucially, the official said Kurdish-dominated forces had stopped moving north towards Jarabulus. “So I think we have put a lid on the Turks’ biggest concern.”

Erdogan said the operation was aimed against both IS and PYD - “terror groups that continuously threaten our country in northern Syria”. “We have said ‘enough is enough’... This now needs to be resolved,” he said.

The Turkish air strikes were the first since a November crisis with Russia sparked when the Turkish air force downed one of Moscow’s warplanes. A dozen IS targets were destroyed in Wednesday’s air strikes. Turkish artillery meanwhile destroyed 70 IS targets, according to Turkish television.

The movements have come at a critical juncture for Turkey in Syria’s five-and-a-half-year war, with signs growing it is on the verge of a landmark policy shift.

Ankara has always called for the removal of President Bashar al-Assad, putting Turkey at odds with his main supporters Iran and Russia.

However Prime Minister Binali Yildirim acknowledged at the weekend for the first time that Assad was one of the “actors” in Syria and may need to stay on as part of a transition. Assad’s government - which has long has little sway in this region - condemned the incursion as a “flagrant violation” of its sovereignty.

The United States is providing Turkey’s military with air cover, intelligence and advisers in its offensive against the Islamic State (IS) group inside Syria , a senior US official said on Wednesday.

“We want to help the Turks get ISIL off the border” between the two countries, the official told reporters, using an alternative acronym for the IS group.

The official was travelling with US Vice President Joe Biden, who arrived in Turkey on Wednesday for meetings with President Recep Tayyip Erdogan and Prime Minister Binali Yildirim, in an effort to help improve relations strained by Turkey’s coup d’etat attempt last month.

US advisers are communicating with the Turkish military about a plan to take the Syrian border town of Jarabulus, a key IS stronghold that is a primary objective of the Turkish offensive , the official said, speaking on condition of anonymity.

The United States is “syncing up with them, our advisers are in the planning cell with them,” he said. “We’ll have close air support if there’s an operation” in Jarabulus.

Washington is also helping ensure that Kurdish fighters further south do not provoke a conflict with Turkish forces by moving north toward Jarabulus, the official said.

The United States has made it clear to the Syrian Democratic Forces, a US-backed Kurdish and Arab alliance, that “we don’t and won’t support them going north, and they can’t without our air cover, so we’ve put a lid on them moving north,” he said.

“I think we’ve put a lid on the Turks’ biggest concern (which) gives us breathing space to make sure the Jarabulus operation is done the right way.”

The Turkish operation - named “Euphrates Shield” - began early Wednesday with Turkish artillery pounding dozens of IS group targets around Jarabulus, according to the Turkish prime minister’s office.

Turkish tanks and special forces accompanied by pro-Ankara Syrian rebels then rolled across the border in an unprecedented operation to drive the IS group out of the town from which it has fired rockets into Turkey .

Pro-Ankara Syrian rebels took the village of Keklijah three miles (five kilometers) west of Jarabulus and two miles from the border, Turkish state media said, in the operation’s first reported military success.