US President Barack Obama said he has decided to take military action against Syria, but will seek authorisation from Congress before he does.
Obama said on Saturday that the US had presented a "powerful case" linking the government of Syrian President Bashar al-Assad to an alleged chemical weapons attack in the Damascus suburbs last week.
"It is a danger to our national security that risks making a mockery of the global prohibition on the use of chemical weapons," he said.
In a brief statement at the White House, Obama said the US military was prepared to launch a "limited
" strike, which analysts say will likely entail firing cruise missiles at Syrian army targets.
"I'm confident we can hold the Assad regime accountable for their use of chemical weapons and deter this kind of behaviour and degrade their capacity to carry it out," he said.
Harry Reid, the Senate majority leader, said there would be a vote on authorising the use of limited military force no later than the week of September 9, when politicians are scheduled to return from recess.
There were some initial critical reactions from senators, notably John McCain and Lindsey Graham, two longtime Syria hawks who said they would not support a military strike that did not try to topple Assad.
“We cannot in good conscience support isolated military strikes in Syria that are not part of an overall strategy that can change the momentum on the battlefield," they said in a statement.
Earlier on Saturday, Russian President Vladimir Putin demanded that the US provide evidence of the Syrian government's alleged use of chemical weapons to the UN Security Council.
He added that it would be "utter nonsense" for the Syrian government to have used such weapons.
Syria has denied carrying out the attack, and Prime Minister Wael al-Halqi said on Saturday that Syria's army is ready for potential foreign strikes against it and has its "finger on the trigger".
Louay Safi, spokesman for the opposition Syrian National Coalition, told Al Jazeera that Obama's statement was a "failure of leadership" and urged the US to act more decisively.
The US is struggling to rally international support for an attack on Syria, and a strong statement from the Arab League would be a boost.
The British parliament rejected a motion calling for military action on Thursday night. The French government, however, still seems committed to military action.
A team of UN weapons inspectors left Syria on Saturday, after finishing gathering evidence about the alleged attacks. The organisation handling the investigation said it could take up to three weeks to finish the analysis.
US officials have already said they will not wait for the results.