MOSCOW - Russia’s envoy to the UN on Friday warned long-term ally President Bashar al-Assad over his vow to retake all of Syria, saying he faced dire consequences if he did not comply with Moscow over the peace process.

“Russia has invested very seriously in this crisis, politically, diplomatically and now also militarily,” Vitaly Churkin told Kommersant daily, referring to an international agreement to cease hostilities sealed in Munich last week. “Therefore we would like Assad also to respond to this,” he said, adding that the Syrian leader’s stance “is not in accord with the diplomatic efforts that Russia is making.”

At their meeting in Munich, the 17-nation group backing Syria’s peace process agreed to work for a ceasefire, the lifting of starvation sieges and the resumption of talks.

In an interview with AFP last week, Assad defiantly pledged to retake the whole of the country, speaking before the plan for a nationwide “cessation of hostilities” in Syria was announced. Asked to comment to journalists on the unusually outspoken criticism of Assad, Kremlin spokesman Dmitry Peskov on Friday said President Vladimir Putin backed the Syrian peace process but stressed that the ceasefire had not yet been implemented. “Everyone including President Putin recognises that there is no alternative other than a political resolution,” he said.

Nevertheless the ceasefire “is now being worked out, discussed. Wait, let’s not run ahead,” Peskov said.

In the interview, Churkin, who has served as Russia’s ambassador to the United Nations since 2006, stressed that if Syria “follows Russia’s leadership in resolving this crisis, then they have a chance to come out of it in a dignified way.” “If they in some way stray from this path - and this is my personal opinion - a very difficult situation could arise. Including for themselves,” he warned.

US and Russian officials met Friday in Geneva to discuss an elusive ceasefire in Syria, but on the ground fighting raged on and Turkey intensified its shelling of Kurdish-led forces. The talks come on the same day that the proposed truce was meant to begin, and are intended to pave the way for a broader meeting on how to implement a cessation of hostilities. The UN’s Syria envoy meanwhile acknowledged that a proposed February 25 date for the resumption of stalled peace talks was no longer “realistically” possible.

Meanwhile, a Kurdish-led alliance backed by US-led strikes seized a stronghold of the Islamic State group in northeastern Syria on Friday, a monitor said. The Syrian Democratic Forces were now in full control of Al-Shadadi in Hasakeh province, the Britain-based Syrian Observatory for Human Rights monitor said.

Saudi Arabia’s foreign minister said Syrian moderate rebels should be armed with surface-to-air missiles against the Russian-backed Assad regime, a German news weekly reported Friday.

Anti-aircraft weapons could tip the scales on the battlefield as they did in Soviet-occupied Afghanistan in the 1980s, Adel al-Jubeir is quoted as saying in an interview with Der Spiegel. “We believe that introducing surface-to-air missiles in Syria is going to change the balance of power on the ground,” he said, stressing this would have to be decided by a coalition of partner states.

Meanwhile, fighting raged on in Syria on Friday, as a hoped-for ceasefire failed to materialise and Turkey intensified its shelling of Kurdish-led forces.

Further dampening hopes for an end to the conflict, the UN peace envoy admitted a February 25 date for a resumption of stalled peace talks was no longer “realistically” possible.

Key regime backer Russia meanwhile warned that recent comments by President Bashar al-Assad about retaking all of Syria were out of step with Moscow’s diplomatic efforts.

On the ground, Turkey intensified its nearly week-long shelling of positions in Aleppo province, where it has sought to halt the advance of a Kurdish-led alliance against rebel forces.

The Syrian Observatory for Human Rights monitor said Ankara’s overnight bombardment was the heaviest since it began targeting the Syrian Democratic Forces (SDF) on Saturday. Turkey also expanded its fire, the Britain-based monitoring group said, hitting the Kurdish town of Afrin for the first time, where two civilians were killed and 28 wounded.

Ankara has been angered by the SDF’s operation in Aleppo province, where it has seized key territory from rebel forces supported by Turkey.

Ankara considers the Kurdish People’s Protection Units (YPG) that dominate the SDF to be an affiliate of the outlawed Kurdistan Workers’ Party (PKK), which has waged a decades-long insurgency against the Turkish state.

It accuses the YPG and PKK of being behind a bombing that killed 28 people in the Turkish capital on Wednesday night, a claim denied by the Syrian Kurdish group.

Ankara fears the SDF advance in Aleppo province is intended to connect Kurdish-held areas in northern and northeastern Syria, creating an autonomous Kurdish region extending along most of its southern border.

Further east, SDF forces were advancing against the Islamic State group in Hasakeh province, the Observatory said.

The monitoring group said the alliance was now just five kilometres (three miles) from the IS stronghold of Al-Shadadi, and had cut two key routes leading from the town to Mosul in neighbouring Iraq and to Raqa, the militants’ de facto Syrian capital.

The advance was assisted by heavy air strikes by the US-led coalition fighting IS, the Observatory said.

The coalition has backed the Kurdish-led SDF against IS, but Washington has cautioned the alliance against taking “advantage” of the situation in Aleppo, wary of angering its Turkish ally.

Ankara is allowing the coalition to fly sorties from its Incirlik base, and has complained several times about Washington’s close relations with the Syrian Kurds.

The Syrian conflict, which began with anti-government protests in March 2011, has become increasingly complex, drawing in several international players.

Key regime backer Russia launched air strikes in support of Assad’s government in September, raising tensions with NATO member Turkey.

Luxembourg’s Foreign Minister Jean Asselborn warned Friday however that Ankara should not count on NATO backing if it provoked Russia into a military confrontation.

“NATO should not allow itself to be dragged into a military escalation with Russia through the latest tensions between Russia and Turkey,” he told Germany’s Spiegel weekly, saying he was speaking on behalf of other NATO members.

Russia’s intervention has allowed Syrian government forces to recapture key territory, including in Aleppo province, where regime fighters have virtually surrounded the rebel-held east of Aleppo city.

In an interview with AFP last week, a confident Assad defiantly pledged to retake all of Syria, but Moscow’s UN envoy said Friday that those comments were “not in accord with the diplomatic efforts that Russia is making.”

Moscow backs a plan announced by 17 world powers last week for humanitarian access throughout Syria and a ceasefire that was to have begun by Friday.

But while aid deliveries have gone ahead to several besieged areas and the United Nations has said it hopes to deliver aid to all 18 within a week, there was no sign on Friday of a ceasefire being implemented soon.

A UN panel co-chaired by Moscow and Washington is charged with working out how to implement the ceasefire, and UN envoy Staffan de Mistura’s office said he would be attending a meeting of the taskforce in Geneva later in the day.

The Munich plan was supposed to pave the way for the resumption next week of peace talks that collapsed earlier this month.

But De Mistura told a Swedish newspaper Friday that he could not “realistically call for new Geneva talks starting on February 25.”

“We need 10 days of preparations and invitations. But we will aim to do this soon,” the Svenska Dagbladet newspaper quoted him as saying.