Obama returns to US to face Congress battle over SyriaPresident Barack Obama has acknowledged he faces an uphill battle to win congressional backing for a military strike against Syria
President Barack Obama has returned to the US from the G20 summit in St Petersburg, which failed to produce international agreement on military action in Syria.
Mr Obama faces a tough week of trying to persuade Congress to authorise military action in response to Syria's alleged use of chemical weapons.
He will also seek public support in a White House address on Tuesday.
Russia restated its opposition to any strike at the G20 summit.
President Vladimir Putin warned that military intervention would destabilise the region.
Both Russia and China, which have refused to agree to a UN Security Council resolution against Syria, insist any military action without the UN would be illegal.
The US accuses President Bashar al-Assad's forces of killing 1,429 people in a poison-gas attack in the Damascus suburbs on 21 August.
Mr Assad and President Putin blame rebels for the attack.'Heavy lift'
President Obama has only a few days to convince Congress, which returns from its summer recess on Monday.
The president is clearing his desk, going all-out to persuade for a vote that he has said is vital for America's credibility, says BBC North America editor Mark Mardell.
Both the Senate and House of Representatives could vote on the Syrian issue as early as next week.
Mr Obama cancelled a work trip to California scheduled for Monday to focus his attention on building support for a resolution to launch a "limited, narrow" strike against Syria.
Before returning to the US, Mr Obama said he would use Tuesday's White House speech to "make the best case I can to the American people as well as to the international community for taking necessary and appropriate action".
"The kind of world we live in and our ability to deter this kind of outrageous misbehaviour is going to depend on the decisions that we make in the days ahead," Mr Obama said.
He earlier acknowledged that he faced a "heavy lift" to win congressional backing.
White House officials have been giving daily classified briefings to congressional members.
A poll commissioned by the BBC and ABC News suggested more than one-third of Congress members were undecided whether or not to back military action - and a majority of those who had made a decision said they would vote against the president.
Many remain concerned that military action could draw the US into a prolonged war and spark broader hostilities in the region.
But the US ambassador to the UN Samantha Power stressed that any intervention would be a "meaningful, time-limited response".
"From the start of the Syrian conflict, the president has consistently demonstrated that he will not put American boots on the ground to fight another war in the Middle East," she said.
"The draft resolution before Congress makes this clear."
The president did not specify what he would do if he did not win the vote.Call for action
Meanwhile, US Secretary of State John Kerry is expected to push for international support for military action during a four-day trip to Europe.
Mr Kerry is to hold talks with EU foreign ministers in Lithuania on Saturday before going on to Paris to meet Arab League representatives. He will then travel to London for further talks with UK Foreign Secretary William Hague.
While the main purpose of the trip had been to push forward Middle East negotiations, Syria is now likely to dominate the agenda, correspondents say.
At the G20 summit, a joint statement from the US and 10 other nations called for a strong international response against President Assad.
But while the UK, Canada and Turkey supported Mr Obama's call for action, the only leaders at the G20 meeting to commit to force in Syria were the US and France.
Mr Obama and Mr Putin held a one-to-one meeting on Syria but failed to reach an agreement.
Some 100,000 people have died in the two-and-a-half-year-old Syrian conflict, according to the UN.