The US says it has started distributing weapons to Kurdish forces fighting so-called Islamic State (IS) in Syria.
Pentagon spokesman Major Adrian Rankine-Galloway said the Kurdish fighters had received small arms and vehicles from the US military.
The weapons aim to help them drive IS from its Syrian stronghold, Raqqa.
Donald Trump this month approved arming fighters from the Kurdish Peoples' Protection Units (YPG), drawing strong condemnation from Turkey.
Turkey views the Kurdish rebels as terrorists and wants to stop them taking more territory in Syria. It is also worried that the weapons will end up in the hands of the Kurdistan Workers Party (PKK), a group it has been fighting for decades.
The Pentagon has previously said it is "keenly aware" of Turkey's concerns, and that the US remains committed to "protecting our Nato ally".
However, the US believes the Kurdish elements of the Syrian Democratic Forces (SDF) will be essential to Raqqa's downfall.
The Pentagon sees them as the most disciplined and organised of the anti-IS groups, says the BBC's Gary O'Donoghue in Washington.
The US has previously supplied light weapons and armoured vehicles to the Arab element of the SDF, known as the Syrian Arab Coalition.
SDF fighters are only 3km (2 miles) from the eastern edge of Raqqa, which is the de facto capital of the caliphate proclaimed by IS in 2014.
US-led coalition air strikes against IS targets have intensified in recent days in preparation for a full assault on the city.
Turkey has not commented publicly on the start of the weapons transfer announced on Tuesday.
The provisions include AK-47s and small-calibre machine guns, according to AFP news agency.
Turkey launched its own offensive last August to push Islamic State militants away from its border and also to stop the advance of local Kurdish fighters.
Last month, its forces carried out air strikes on YPG positions in Syria which it described as "terrorist havens".