Syria's rebels have seen an influx of arms including anti-tank weaponry for their fight against President Bashar Al Assad regime, in an effort coordinated with the help of the United States, a report said Wednesday.

Officials in President Barack Obama's administration insist it is not directly supplying the weapons or providing funding, with some Arab states paying for the new arms, the Washington Post said, citing US and foreign officials.

But Washington has stepped up links with the rebels and regional militaries allying with them, playing a role in the rebel's foreign support network, the report said.

"We are increasing our non-lethal assistance to the Syrian opposition, and we continue to coordinate our efforts with friends and allies in the region and beyond in order to have the biggest impact on what we are collectively doing," a senior State Department official told the Post on condition of anonymity.

The US administration's move to increase contact with the rebels, and boosting information sharing with Arab states who back them, is a shift in policy that up until now has resisted overt support for the armed groups battling Assad forces, the Post said.