A US decision to provide arms to Syrian Kurdish fighters has been criticised by Turkey's top diplomat.
The US announced on Tuesday that it would arm Syrian Kurdish fighters, which it said was a necessary step to recapture the Islamic State stronghold of Raqqa.
The move came despite opposition from Turkey, which views the group as an extension of the Kurdish insurgency in its south-east.
During a visit to Montenegro on Wednesday, Turkish foreign minister Mevlut Cavusoglu said there was no difference between the Syrian Kurdish fighters and the outlawed Kurdish rebels fighting Turkey.
"Every weapon that reaches their hands is a threat towards Turkey," Mr Cavusoglu said.
Mr Cavusoglu said President Recep Tayyip Erdogan would take up the issue with President Donald Trump during a visit to Washington planned for next week.
However, the Syrian Kurdish group labelled a terror organisation by Turkey hailed the US decision to arm it with heavy weapons to fight IS.
The YPG militia said the decision is "historic" and a "sign of confidence" in the group, in a statement released on Wednesday.
Turkey's deputy prime minister Nurettin Canikli denounced the decision as "unacceptable" and said it "amounts to support to a terror organisation".
"The Trump administration providing arms to a terrorist organisation - either directly or indirectly through the YPG - does not change the fact that this amounts to support to a terror organisation." Mr Canikli said.
The YPG said the US commitment to the group, and its umbrella coalition the Syrian Democratic Forces, will allow it to expand its operations against IS.
It said the decision is a refutation of the "distortions" likening the YPG to a terror organisation.
Ilham Ahmed, a top official in the Syrian Democratic Forces' political office, said the decision to provide heavier arms carries "political meaning" and "legitimises the YPG and the Syrian Democratic Forces".
She said the decision is likely to be met with "aggression" from Mr Erdogan.
The SDF's rapid advance against IS last year prompted Turkey to send ground forces across the border for the first time in the six-year civil war to help allied Syrian forces battle IS and halt the Kurds' progress.
Since then, Turkey is believed to have positioned more than 5,000 troops in northern Syria, and has escalated its air strikes and cross-border artillery attacks against Kurdish forces.
A Turkish air raid in late April killed 20 YPG fighters and media officials, prompting the US to deploy armoured vehicles along the border in a show of support for the group.
Mr Canikli expressed hope that Washington would reverse its decision, saying "there is no truth to the claim that the fight against Daesh can only be successful with the YPG".