ISTANBUL - Turkey on Wednesday slammed as unacceptable a US plan to arm Syrian Kurdish fighters whom Ankara considers terrorists, but the militia applauded a "historic" move that would speed up the defeat of Islamic State (IS) extremists.

The issue risks further stoking tensions between Ankara and Washington less than a week before President Recep Tayyip Erdogan heads to Washington to meet his US counterpart Donald Trump, in their first face-to-face encounter as heads of state.

Tayyip Erdogan on Wednesday called on the United States to immediately reverse a decision on arming Syrian Kurdish fighters considered by Ankara to be a terror group. "I hope very much that this mistake will be reversed immediately," Erdogan said after Washington announced it would arm the Kurdish Peoples' Protection Units (YPG) in the fight against jihadists in Syria.

Erdogan vowed to bring up the issue in talks with US President Donald Trump on May 16 in Washington, their first face-to-face encounter as heads of state.

"I will personally express our worries in a detailed way when we talk with President Trump on May 16," he added, saying the issue would also be discussed at the NATO summit in Brussels on May 25. The Kurdish Peoples' Protection Units (YPG) is seen by Washington as the best ally against Islamic State group jihadists in Syria and the prime attacking force in any upcoming assault on their stronghold of Raqa.  But Ankara regards the YPG as a terror group and the Syrian branch of the Kurdistan Workers' Party (PKK), which since 1984 has waged an insurgency inside Turkey leaving tens of thousands dead.

The dispute poisoned ties between the two NATO allies under the administration of former president Barack Obama but Ankara had hoped for smoother ties under Trump. Prime Minister Binali Yildirim said it was "out of the question" for Turkey to accept any direct or indirect help for the PKK. "The United States and Turkey are two major partners in NATO. We don't believe America would choose a terror group over our strategic relations," he told reporters. Speaking to A Haber television, Deputy Prime Minister Nurettin Canikli slammed any supply of arms to the YPG "unacceptable". "We expect that this mistake is to be rectified," he said.

Turkish Foreign Minister Mevlut Cavusoglu added that "every weapon that turns up in their hands is a threat directed toward Turkey".

The Syrian conflict is “unwinnable”, Antonio Guterres said on Wednesday in his first speech in Britain since taking over as UN Secretary General. “It is high time to understand that this is a war where nobody is winning and this is a war which is becoming a danger to all of us” by boosting regional instability and international terrorism, he said.

“There will only be peace in Syria or in any of the other conflicts that we are witnessing when the parties to the conflict understand that they cannot win,” he said, listing also the conflicts in Libya, South Sudan and Yemen.



Pentagon chief Jim Mattis sought to allay Turkish concerns, saying at a news conference in Lithuania the US would work very closely with Turkey over security on its border with Syria. "We have very open discussions about options and we will work together, we will work out any of the concerns," he said.

In a surprise announcement, the Pentagon had said Trump had authorised the arming of Kurdish fighters within the Syrian Democratic Forces (SDF) "to ensure a clear victory over ISIS in Raqa".

The YPG hailed the move as "historic" and said it would now play "a more influential, powerful, and decisive role" in fighting IS.

YPG spokesman Redur Xelil described the move as "somewhat late", but would still "provide a strong impetus" to all forces fighting IS.

The SDF, a US-backed group dominated by YPG but which also contains Arab elements, said that receiving US arms and military equipment would "hasten the defeat" of the jihadists. It remains to be seen what shadow the issue will cast over the talks between Trump and Erdogan, which have been touted as chance to forge a new partnership between the two NATO allies.  While the government expressed predictable anger, the deputy head of the opposition Republican People's Party (CHP) Ozturk Yilmaz said it should go even further by postponing Erdogan's visit to the US. A high-level Turkish delegation including Chief of Staff General Hulusi Akar, presidential spokesman Ibrahim Kalin and Turkey's spy chief Hakan Fidan had been in the US laying the groundwork for the meeting.

According to the New York Times, the delegation was informed of the decision to arm the YPG by Trump's national security adviser H.R. McMaster.

Turkish media said the three met McMaster at the White House on Monday but gave no details over the content of the talks.

Both Washington and Brussels classify the PKK as a terror group but do not regard the YPG as such.

But Cavusoglu said the two were one and the same.

"YPG and PKK are both terror groups, there is no difference at all between them. They only have different names," he said.

Turkey has said it is keen to join the battle to recapture Raqa but on condition the offensive does not include the YPG

Last month, Erdogan said if Turkey and the United States joined forces, they could turn Raqa into a "graveyard" for jihadists.

But on April 27, Turkish warplanes struck YPG forces in Syria and also hit Kurdish forces in neighbouring Iraq in what Ankara described as "terrorist havens".

Meanwhile, Trump was to receive Russia's top diplomat Sergei Lavrov at the White House on Wednesday to discuss a Russian plan to establish safe zones in Syria and help end the six-year conflict.

Russia - the key ally of Syrian President Bashar al-Assad - and Turkey have been on opposite sides of the Syrian conflict but are working increasingly closely together in search of peace.