In a brief readout of the approximately 30-minute meeting, a Pentagon statement said the two men discussed a range of bilateral security issues.

"The secretary reiterated US commitment to our NATO ally," stated the readout, provided by Pentagon spokeswoman Dana White.

"Both leaders affirmed their support for peace and stability in both Iraq and Syria."

It was not immediately clear if the leaders discussed President Donald Trump's decision this week to arm the Kurdish YPG, who are fighting the Islamic State group in Syria.

The move announced on Tuesday has already provoked fury in Turkey, which says the YPG are linked to its own domestic Kurdish separatist group the PKK, or Kurdish Workers Party.

A first consignment of weapons is already in place for delivery and could be dispatched to the Kurds "very quickly", US Colonel John Dorrian said Wednesday.

Mattis and Yildirim met ahead of the start of a Somalia conference in London.