Dozens of US lawmakers are calling on President Barack Obama to consult with Congress and gain its approval before intervening militarily in Syria.

The United States is poised to launch a military strike on Syria in coming days after determining that President Bashar al-Assad's regime used chemical weapons during an attack outside Damascus last week which killed hundreds of civilians.

Several lawmakers sought to put the brakes on what Republican congressman Scott Rigell, who drafted the letter to Obama, said could be potential abuse of presidential authority if he decides to attack Syria without a congressional green light.

Congress is on recess until September 9, but "members can reconvene at your request," Rigell wrote in his letter, which as of late Tuesday had 40 rank-and-file co-signers including six Democrats.

"We stand ready to come back into session, consider the facts before us, and share the burden of decisions made regarding US involvement in the quickly escalating Syrian conflict."

Rigell and others are bristling at a possible executive order of use of force without the House and Senate weighing in, as was the controversial case in Libya.

While decrying the use of chemical weapons as "beyond the pale," House Foreign Affairs Committee chairman Ed Royce warned that US intervention could trigger an "escalation" of the Syria crisis.

The Obama "administration should come to Congress to explain their plans," Royce said.

"The consequences are too great for Congress to be brushed aside."

The 1973 War Powers Resolution sought to compel presidents to seek congressional approval in order to deploy US troops in "hostilities" lasting beyond 60 days.

Most presidents have neglected to ask for such permission, instead simply notifying Congress.

White House spokesman Jay Carney said Tuesday it is consulting with members of Congress, and lawmakers including House Speaker John Boehner have acknowledged being briefed on potential action.

Carney did not specify whether Obama would seek congressional approval for a US strike, which experts believe will come in the form of cruise missiles targeting Syria's military facilities.

But Democrats and Republicans alike expressed reservations about large-scale military action, warning of regional instability and potential anti-American fallout at a volatile time in the Middle East.

"While the use of chemical weapons is deeply troubling and unacceptable, I believe there is no military solution to the complex Syrian crisis," Democrat Barbara Lee said.

"Congress needs to have a full debate before the United States commits to any military force in Syria - or elsewhere," the congresswoman said.

Some, such as Republican Senators John McCain and Lindsey Graham and Senate Democrat Bill Nelson, advocate a military strike, but others remain reserved.

Carney dismissed the idea that regime change was a rationale for intervention, but Rigell sought clarity from the administration over what it expects down the road.

"What does this look like a month out, six months out, a year out?" Rigell told AFP.

He said the skepticism in Congress about shaping the outcome of the Syria conflict was "warranted" given the many unknowns there, including how any post-Assad regime would treat the United States.