Britain's government said on Monday that it had "no plans" to hold a second parliamentary vote on joining military action against Syria even if the US Congress approves air strikes next week.

Prime Minister David Cameron lost a vote in the lower House of Commons on Thursday on the principle of taking action to punish Syria for alleged chemical weapons use, and pledged to respect parliament's wishes.

But after US President Barack Obama announced on Saturday that he would ask Congress to authorise military action against Bashar al-Assad's regime there has been pressure on Cameron to hold a fresh vote.

Cameron's official spokesman said on Monday: "Parliament has spoken and that is why the government has absolutely no plans to go back to parliament."

"The position we are in is that parliament has expressed its will and that is the basis on which we will proceed," added the spokesman.

Deputy Prime Minister Nick Clegg, whose Liberal Democrats are in coalition with Cameron's Conservatives, said meanwhile he could "not foresee any circumstances" under which the government would seek a second vote.

"We're not going to keep asking the same question of parliament again and again," Clegg said. "I can't foresee any circumstances that we would go back to parliament on the same question, on the same issue."

But the careful wording of the government's statements left room for supporters of military action against Syria to keep pressing for a new vote once US lawmakers have decided.

Former international development minister Andrew Mitchell said nothing should be ruled out.

"It may be, after lengthy and careful consideration, (that) Congress affirms its support for the president's plans and, in the light of that, our parliament may want to consider this matter further," he told BBC radio.

The US Congress is to debate Obama's decision to attack Syria during the week starting on September 9 when they return to work, its speaker said.

Obama cited the British vote when defending his decision to let US lawmakers vote.

Cameron suffered the most humiliating defeat of his three years in power when Conservative rebels joined the opposition Labour party in voting against military action by 285 to 272.

Labour leader Ed Miliband had called for "compelling" evidence that Assad's regime had gassed its own people before launching an attack.

Cameron's spokesman said the prime minister would keep pressing for a political solution to the Syria conflict at the G20 meeting of world leaders in Saint Petersburg later this week.