Turkey today slammed as 'unacceptable' a US announcement that Washington would supply arms and military equipment to Kurdish fighters battling Islamic State jihadists in Syria.

Istanbul: Turkey on Wednesday slammed as "unacceptable" a US announcement that Washington would supply arms and military equipment to Kurdish fighters battling Islamic State jihadists in Syria.

"The supply of arms to the YPG is unacceptable," Deputy Prime Minister Nurettin Canikli told A Haber television. "Such a policy will benefit nobody".

"We expect that this mistake is to be rectified," he said, days ahead of a crunch meeting in Washington between President Recep Tayyip Erdogan and US counterpart Donald Trump.

The Kurdish Peoples' Protection Units (YPG) has been seen by Washington as the best ally against jihadists in Syria.

But Ankara regards the group as a terror outfit, as it does the Syrian branch of the Kurdistan Workers' Party (PKK), who have waged an insurgency since 1984 inside Turkey that has left tens of thousands dead.

Trump on Monday "authorised the Department of Defence to equip Kurdish elements of the Syrian Democratic Forces as necessary to ensure a clear victory over ISIS in Raqa," Pentagon spokeswoman Dana White said in a statement.

The weapons are being delivered for use by Kurdish fighters ahead of the upcoming offensive to recapture Raqa, the last major bastion for IS in Syria.

The US announcement came just ahead of Erdogan's visit to Washington next week for talks with Trump, the first time the two men will meet as heads of state.

A Turkish high-level delegation made up of Chief of Staff General Hulusi Akar, presidential spokesman Ibrahim Kalin and Turkey's spy chief Hakan Fidan have already been in the US to lay the groundwork for the visit.

Turkey has said it is keen to join the battle to recapture Raqa but on the condition that the offensive does not include the Syrian Kurdish fighters.

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