Robert Ford's words come a day after John Kerry described as “possible” a meeting with Syria’s biggest rebel alliance.

The US ambassador to Damascus has said a newly formed Islamist alliance in Syria has refused to meet with American officials, in an interview aired on Wednesday on Al Arabiya television.

“The Islamic Front has refused to sit with us without giving any reason,” Robert Ford said, a day after US State Secretary John Kerry described as “possible” a meeting with Syria’s biggest rebel alliance.

“We are ready to sit with them because we talk to all parties and political groups in Syria,” Ford was quoted as saying on the Dubai-based channel’s Arabic website.

Ford returned to Washington in February 2012 after rising security problems forced the closure of the US embassy in the Syrian capital.

Six opposition groups came together last month to form the Islamic Front, which brings together tens of thousands of fighters and seeks to oust President Bashar Al Assad and establish an Islamic state in Syria.

Last week, the Front overran the northern headquarters and two warehouses belonging to the US-backed Free Syrian Army, prompting Washington to cut off non-lethal aid to the main secular military opposition in the north.

In Washington, State Department deputy spokeswoman Marie Harf said earlier that if a meeting with the Front did take place, the United States would expect the return of its stolen non-lethal assistance.

Washington has said it is already meeting with a broad section of Syrian groups to try to end the nearly three-year war through negotiations, but has explicitly ruled out any contacts with those linked to Al Qaeda or designated as terrorists by the US.

Last month, the Islamic Front said it wanted to set up an Islamic state in Syria, but insisted it would protect minorities and not create an “oppressive, authoritarian system”.

Syria’s uprising began as a series of peaceful pro-democracy protests in March 2011, but a brutal regime crackdown ignited a full-blown civil war in which hardline Islamist groups have taken on an increasingly prominent role.