US President Barack Obama is lobbying sceptical lawmakers as they weigh up whether to support military strikes against Syria.
Obama, as well as Vice President Joe Biden and the White House chief-of-staff, all made calls to members of the House and Senate, according to a senior White House official.
That came on top of a classified briefing held for members of Congress on Capitol Hill on Sunday afternoon that, according to the official, drew some 70 lawmakers.
On Saturday, the White House formally asked Congress for authorisation to conduct military strikes in Syria in a draft resolution framing a narrow set of operations.
That came on the heels of a surprise announcement by Obama that he will seek approval from the House and Senate for action against Syria's alleged use of chemical weapons.
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It remains to be seen if war-weary lawmakers will endorse Obama's push for action, or hand him a bitter defeat.
On Monday, a federal holiday, Obama will host influential Republican John McCain at the White House.
McCain indicated on Sunday he was not yet sure he would support a vote on the resolution.
"We're in a bit of a dilemma here because I think Senator Lindsey Graham and I, and others, will be wanting a strategy, a plan, rather than just we're going to launch some cruise missiles and that's it," he told CBS television.
More phone calls to members of Congress are slated for Monday, as is a conference call with administration officials for House Democrats, the official said.
Then on Tuesday, before leaving for Stockholm and a G20 meeting in Russia, Obama will host the top Republicans and Democrats on key congressional committees that deal with national security issues.
