The move, ahead of the first official visit by the head of the National Coalition Ahmad Jarba, aims "to empower the Syrian opposition and bolster its efforts to assist people who need help inside Syria," a senior US administration figure claimed.

Washington is boosting its support and speeding up military deliveries to those militant groups fighting against army.

"This is an important step in the path toward a new Syria, its recognition on the international stage, and its relations with Syrian nationals in the US," Jarba claimed, as his delegation began arriving in Washington.

Jarba will be accompanied on his eight-day trip to the United States by the new chief of staff of the Free Syrian Army (FSA), Brigadier General Abdelilah al-Bashir, his office said last week.

"He will meet US officials to discuss the supply of sophisticated weapons to the FSA to enable it to change the balance on the ground," his office said.

US officials on a conference call with reporters refused to be drawn on the type of non-lethal aid or weapons being supplied by Washington.

But the senior official acknowledged that there was "an asymmetry militarily" between the opposition militants and the army of President Bashar al-Assad they are fighting to overthrow.

The move to recognize the Syrian Opposition Coalition offices, which will not give the staff diplomatic immunity, comes after a peace process known as Geneva II collapsed in February amid bitter recriminations.

The US along with many EU allies recognized the Syrian coalition as the legitimate representative of the Syrian people in late 2012.

Washington in March shuttered the Syrian embassy in the US capital, prompting an angry response from Damascus.

NJF/NJF