The United Nations Security Council on Saturday approved the expansion of the UN ceasefire observer force in Syria from 30 to 300.
The council also demanded an "immediate halt to the violence," which has escalated rather than abated since Syria's government and opposition agreed to halt hostilities more than a week ago.
The resolution is the first authorizing unarmed UN military observers to go into a conflict area, giving Secretary-General Ban Ki-moon authority to decide when to deploy the additional monitors.
Ban's approval is expected to be based on "developments on the ground" including "the consolidation of the cease-fire."
The resolution came after the UN leader on Thursday pressed the Security Council to to take "early action" to send 300 unarmed observers to Syria to monitor a shaky cessation of hostilities that commenced on April 12.
"This is not a decision without risk," he acknowledged. "But I believe it can contribute to achieving a just peace and political settlement, reflecting the people's will in Syria."
Ban told reporters there was "deeply troubling evidence" that the government was pursuing its deadly crackdown despite agreeing to halt violence.
"The past few days, in particular, have brought reports of renewed and escalating violence, including the shelling of civilian areas, grave abuses by government forces and attacks by armed groups," he explained.
In a statement released ahead of the Security Council meeting on Saturday, Ban again demanded that Syria end all violence and "the gross violations of the fundamental rights of the Syrian people."
He also demanded Syrian President Bashar al-Assad "send its troops and heavy weapons back to their barracks" in accordance with a UN-backed peace plan brokered by UN-Arab League special envoy Kofi Annan.
Saturday's resolution merged rival Russian and European texts and dropped a European threat of non-military sanctions against Syria. Instead it expresses the council's intention to “consider further steps."
However, US ambassador to the United Nations Susan Rice warned that if Syria doesn't implement all its commitments or obstructs the work of the monitors that Washington would "pursue other measures."
Analysts say "other measures" in diplomatic language is generally a reference to sanctions.
"Let there be no doubt, we, our allies and others in this body are planning and preparing for those actions that will be required of all of us if the Assad regime persists in the slaughter of the Syrian people," she said.
She added the US would not wait 90 days to pursue such measures should the Assad regime continue the brutal 13-month crackdown in Syria that has claimed at least 9,100 civilian lives.
Syrian UN ambassador Bashar Jaafari claimed on Saturday that his government had informed Annan it has "withdrawn troops and heavy weapons from urban centers."
He did not, however, specify when or where the purported pullback took place. He said "police and other security forces will maintain law and order" and "exercise the utmost degree of restraint."
Jaafari – who insisted the Assad regime would continue to strike at "foreign terrorists," which has been regime code for domestic dissidents and rebels – said Syria has "demonstrated considerable cooperation" with Annan and his plan.
Rice responded that the United States is "sober about the risks, all the more so given the Assad regime's long record of broken promises, deceit and disregard for the most basic standards of humanity."
"The Syrian people, like us, know that the deployment of 300, or even 3,000 unarmed observers cannot on its own stop the Assad regime from waging its barbaric campaign of violence against the Syrian people," she said.
"What can bring a halt to this murderous rampage is continued and intensified external pressure on the Assad regime," she added.
Despite repeated US demands that Syrian President Bashar Assad step down, the Obama administration maintains Assad has a firm hold on power and that military force would be required to oust him.
Nonetheless, US secretary of state Hillary Clinton has ruled out providing military aid to the rebel Free Syrian Army or direct military intervention.