US President Barack Obama won his first major victories on securing Congress support for strikes on Syria, with senior members on both sides of the House of Representatives saying they would back him.

The House speaker and top Republican in Congress, John Boehner, said on Tuesday that he would support the president's motion for strikes against the regime of Bashar al-Assad for the alleged use of chemical weapons, and called on his party colleagues to support the president.

"We have enemies around the world that need to understand we are not going to tolerate this type of behavior," Boehner said.

His Republican colleague, house majority leader Eric Cantor, also supported Obama's call.

Nancy Pelosi, the Democratic Party's leader in the house, said she did not believe Congress would reject Obama's call, and that Assad's action was "behaviour outside the circle of civilised human behaviour and we must respond''.

She did, however, say that the public needed to hear more of the intelligence gathered against Assad.

The politicians' statements came after a meeting at the White House, where the president said he was confident of securing Congress support for military action.

"What we are envisioning is something limited. It is something proportional. It will degrade Assad's capabilities," Obama said.

"At the same time we have a broader strategy that will allow us to upgrade the capabilities of the opposition," he said.

Later, the US secretary of state, John Kerry, and Chuck Hagel, the defence secretary, gave evidence to the Senate foreign relations committee, where they were pressed on whether the resolution put to Congress would explicitly rule out the use of ground troops.

Kerry said the language of the resolution was still being worked out, but it was important to leave options open for using troops in a scenario where "Syria imploded" and stockpiles of chemical weapons needed to be secured from extremists.



"I don't want to take off the table an option that might or might not be available to the president of the United States to secure our country," he said at the hearing.



When some senators objected, Kerry said the administration would work with Congress to draft a resolution that addressed concerns about the possible use of ground troops.



"I know the administration has zero intention of putting troops on the ground and within the confines of this

authorisation, I'm confident we'd have zero problem with including some kind of prohibition there if that makes you comfortable," he told the senators.

Hagel told senators that regional allies strongly supported US action against the Assad regime.

Also on Tuesday, the UN secretary-general Ban Ki-moon said that military action was only justified if in self-defence or with a UN mandate.

"The use of force is lawful only when in exercise of

self-defence in accordance with Article 51 of the United Nations Charter and, or when the Security Council approves such action."

But he said the UN Security Council should unite if it was proved that chemical weapons were used in Syria by any side.

"If confirmed, any use of chemical weapons by anyone under any circumstances will be a serious violation of international law and outrageous war crime," he said in a video statement. "Any perpetrators must be brought to justice. There should be no impunity."