US Secretary of State Hillary Clinton has warned the Syrian regime to "stop killing" its citizens or face what she described as "serious consequences".
"There is no more time for excuses or delays ... this is a moment of truth," said the Secretary of State after a meeting of the 83-country "Friends of Syria" conference.
Earlier, Mrs Clinton said: "Nearly a week has gone by, and we have to conclude that the regime is adding to its long list of broken promises."
"The world must judge Assad by what he does, not by what he says."
"And we cannot sit back and wait any longer."
Mrs Clinton and Foreign Secretary William Hague have accused President Bashar al Assad of breaking his promise to implement a UN-Arab League peace plan by launching new attacks against opponents.
Western and Arab nations have been meeting in Istanbul, Turkey, for the second conference of the "Friends of Syria" to discuss ways to support the opposition and put more pressure on the regime.
But Damascus' allies Russia and China - who blocked a previous UN Security Council resolution calling for the leader to stand down - did not attend the talks.
The Istanbul conference called on UN-Arab League special envoy Kofi Annan to set a timeline for next steps to persuade Mr Assad to end the conflict, including a return to the Security Council, if the killing continues.
Mr Annan's plan calls for violence to stop, a daily two-hour humanitarian ceasefire and access to all areas affected by the fighting.
It also wants an inclusive Syrian-led political process, a right to demonstrate, and the release of people detained arbitrarily.
Mr Hague accused Mr Assad of "stalling for time" and warned if the issue does go back to the Security Council, he may no longer be able to rely on the backing of Moscow and Beijing.
Delegates say Saudi Arabia and other Gulf countries are creating a multi-million dollar fund to pay salaries to members of the rebel Free Syrian Army and soldiers who defect from the regime and join opposition ranks.
The plan is the first formal support, though only financial, for Syria's rebels.
Delegates suggested it offers a solution to the international divide over whether to arm the rebels or support them through only non-lethal or humanitarian means.
But it was unclear how the fund would be set up and monitored.
Some fear putting weapons in rebel hands would lead to a civil war after the year-long uprising.
Saudi Arabia had earlier announced it is a "duty" to arm opposition groups as the Damascus regime declared a defeat of rebel forces.
As well as calling for tighter sanctions, Mrs Clinton announced an extra \$12m (£7m) in humanitarian aid, bringing to \$25m the total US contribution so far.
She also backed opposition efforts to bring about a democratic and broad vision for a future Syria .
The US said it would work with international partners to gather evidence that can be used to hold perpetrators of abuses to account.
America will "train Syrian citizens working to document atrocities, identify perpetrators, and safeguard evidence for future investigations and prosecutions," Mrs Clinton said.
UN officials estimate more than 9,000 people have died since Mr Assad began crushing pro-democracy protests last March.