BEIRUT — A top Syrian Kurdish official on Wednesday welcomed the U.S. decision to arm Kurdish fighters with heavier weapons, saying it would “legitimize” the force as it prepares to march on Raqqa, the de facto capital of the Islamic State group.

But Turkey’s Deputy Prime Minister Nurettin Canikli said the decision, announced by the Trump administration Tuesday, was “unacceptable.”

The U.S. said it would provide heavier arms to the Kurdish-led Syrian Democratic Forces, which have driven IS from much of northern Syria with the help of U.S.-led airstrikes, and are among the most effective ground forces battling the extremists.

Ankara says the Kurdish militia known as the YPG, which forms the backbone of the force, is an extension of the Kurdistan Worker’s Party, or PKK, which has been waging a decades-old insurgency in Turkey and is considered a terrorist group by Turkey, the U.S. and other Western countries.

“The Trump administration providing arms to a terrorist organization — either directly or indirectly through the YPG — does not change the fact that this amounts to support to a terror organization.” Canikli told Turkey’s A Haber television.

Ilham Ahmed, a top official in the Syrian Democratic Forces’ political office, said the decision to provide heavier arms carries “political meaning” and “legitimizes the YPG and the Syrian Democratic Forces.”

She said the decision is likely to be met with “aggression” from Turkish President Recep Tayyip Erdogan, who is to visit Washington next week.

The SDF’s rapid advance against IS last year prompted Turkey to send ground forces across the border for the first time in the more than six-year-old 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 airstrikes and cross-border artillery attacks against Kurdish forces.

A Turkish air raid in late April killed 20 YPG fighters and media officials, prompting the U.S. to deploy armored vehicles along the border in a show of support for the group.

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.” Daesh is the Arabic acronym for IS.