Though the supply came under the administration of President Donald Trump, it was allowed by rules first enacted by his predecessor Barack Obama.

"We have provided armored Sport Utility Vehicles to the Syrian Arab Coalition using existing authorities, in the interest of helping protect our partnered force from the (IS) improvised-explosive device threat," US military spokesman Colonel John Dorrian told AFP.

"The decision was made by military commanders, and has been in the works for some time," Dorrian said.

A US official said the decision to supply the vehicles pre-dated the Trump administration, but on the ground it was being interpreted as a sign of new support.

"It was a ground-level tactical decision, it's not a policy-type decision, it's a tactical decision based on the threats the SDF might be facing," Pentagon spokesman Eric Pahon said.

"We are providing them with the tools to face whatever the current threat is."

The Syrian Arab Coalition is a component of the broader Syrian Democratic Forces, the bulk of whose fighters are Kurdish.

The Pentagon has previously supplied the Arab component with light weaponry and ammunition, and has sent US and other Western special forces as "advisers" to help the SDF as a whole.

"We have provided (the Arab component with) equipment for some time, but this is the first delivery of up-armored SUVs," Dorrian said.

Earlier Tuesday, SDF spokesman Talal Sello told AFP that "American armored vehicles" had arrived for the SDF for the first time.

"This happened after the new US administration came to power," Sello said.