The U.S. military will move forward "very quickly" with plans to distribute weapons and ammunition to Kurdish YPG fighters battling the Islamic State in Syria despite opposition from NATO ally Turkey, a Pentagon spokesman said Wednesday.

"We've got a certain amount of supply in the country already that was used to equip the Syrian Arab Coalition and some of that may be distributed very quickly," Air Force Col. John Dorrian, a spokesman for Operation Inherent Resolve, the U.S.-led campaign against ISIS, told Pentagon reporters.

Dorrian said he did not have an exact timeline detailing when the Kurdish fighters would receive the weapons, but said any equipment provided by the United States would be "metered out" and aligned with specific tasks involved in the operation to retake Raqqa, the de facto capital of ISIS's self-proclaimed caliphate.

The weapons going to the YPG will include machine guns, mortars, small arms, and ammunition, Dorrian said.

President Donald Trump approved arming the Syrian Kurdish militia this week to support the U.S.-led offensive in Raqqa.

The decision received immediate pushback from Turkish President Recep Tayyip Erdogan, who regards the YPG as an extension of the Kurdistan Workers' Party, or the PKK, which is considered a terrorist group by both Ankara and Washington. Erdogan accused the Trump administration on Wednesday of siding with terrorists.

Trump will meet with Erdogan next week in Washington ahead of next month's NATO summit.

Dorrian said providing arms to the YPG will "accelerate" the offensive on Raqqa, where the U.S. military estimates about 4,000 ISIS fighters remain. He said U.S.-led forces had "almost completely" isolated Raqqa and expected troops to soon begin advancing "within striking distance" of the city. He did not offer a timeline detailing when the offensive will begin for security reasons.

"We want to let the enemy worry about when our partner forces are going to start, but in the meantime the coalition will continue hammering the enemy anywhere that they can be found as preparatory fires and shaping efforts to help pave the way for the liberation of the city," he said.

Jim Phillips, senior research fellow for Middle Eastern affairs at the Heritage Foundation, said the move will anger Turkey ahead of its White House visit next week.

"The administration’s decision to arm the Syrian Democratic Forces, which are predominantly Kurdish, makes military sense, but will aggravate Turkey," Phillips said. "The Kurds have been the most effective fighters against ISIS in Syria, but unfortunately they are anathema to Turkey, which sees them as an extension of the Kurdistan Workers’ Party, a Kurdish separatist group that Turkey has battled since 1984. This issue is likely to come up when Turkish President Erdogan visits the White House next week."

ISIS has controlled Raqqa since early 2014. Military officials have argued for months that the YPG is the only force on the ground capable of forcing ISIS out of Raqqa in the near future.