SANAA, SYRIA — A crowd of young Syrian fighters lined up behind a pickup truck to receive their equipment: an AK-47 and a load of ammunition.

The battlefield gear was their reward for completing a 20-day course led by American Special Forces in northern Syria in how to fight the Islamic State.

They will need much heavier weapons, however, if they want to evict the militants from Raqqa, the self-styled capital of the Islamic State. And facing objections from Turkey, the Trump administration has yet to say when and whether it would provide them.

This is a critical moment for the Syrian Democratic Forces, which the American military says is 50,000 strong and which it has nurtured to roll back the Islamic State, also known as ISIS and ISIL.