Jim Mattis

"This is a coward and he is not a man by any definition that we use in the Department of Defense," US Defense Secretary Mattis said.

“I can see how it might start, but I am not sure when or where,” the secretary told lawmakers.

A list of potential buyers being given fast-track treatment is expected to expand to include more NATO members, Saudi Arabia and other Gulf partners as well as allies such as Japan and South Korea.

Reconciliation, Mattis said, was "almost an equal priority of my interest going in."

Secretary of Defense Jim Mattis chided Moscow for partnering with Assad, suggesting it might even be a partner in the Syrian government's strikes on civilians.

"They don't have to wait until their citizens are dying under attack before they actually address that issue," he said about Israel.

Qatar has broken its isolation not only in the region through outreach to Iran and Turkey but also in Washington, illustrating how it put together a successful strategy.

Turkey's four-day-old campaign aims to crush US-backed Kurdish YPG fighters in an air and ground offensive on Syria's Afrin region and has opened a new front in Syria's multi-sided civil war.

US Defense Secretary Jim Mattis says US is shifting to stabilizing eastern Syria, which will mean more diplomats and contractors.

This is the first time the US defense secretary has said that there would be an increase of diplomats in the parts of the country retaken from Islamic State militants.