The U.N. Security Council has authorized the deployment of up to 300 unarmed monitors to Syria, where deadly violence has marred a week-old ceasefire between the government and opposition forces.

The council unanimously passed a resolution on Saturday authorizing the observer mission for an initial period of 90 days.

The measure gives U.N. chief Ban Ki-moon authority to make an “assessment” on whether its safe to deploy monitors. His assessments will be based on developments in Syria that include a cessation of violence.

Mr. Ban welcomed the vote and urged Syrian President Bashar al-Assad's government and “other parties” to swiftly create the conditions needed for the deployment. In a statement, he said the “challenges on the ground are serious.”

After the vote, U.S. ambassador Susan Rice accused Syria of “broken promises” and “deceit” and said the monitoring mission, alone, could not halt unrest in the country.

“The Syrian people, like us, know that the deployment of 300, even 3000 unarmed observers can not on its own stop the Assad regime from waging a barbaric campaign of violence against the Syrian people. What can bring a halt to this murderous rampage is continued and intensified external pressure on the Assad regime.”

Syria's U.N. ambassador, Bashar Ja'afari, welcomed the arrival of more monitors. However, he accused the international community of continuously accusing his government of violence while ignoring crimes committed by armed opposition groups.

The Syrian government and opposition forces agreed to a cease-fire as part of a peace plan brokered by U.N.-Arab League envoy Kofi Annan. But, the two sides have repeatedly accused each other of violating that agreement.

The opposition Syrian Revolution General Commission says “regime fire” killed at least four people in Syria on Saturday. Also, activists say explosions rocked a military airport near the capital.

Meanwhile, the government said “armed terrorists” planted an explosive device near a pipeline in the eastern Deir el-Zour province on Saturday. The government has blamed armed groups for a string of attacks against security forces over the past few days.

The Security Council had already approved an advance team of 30 monitors but analysts say many more observers are needed to carry out the U.N. mission.

Syria's state-run SANA news agency says monitors visited the flashpoint city of Homs, on Saturday, where they met with the regional governor and toured several neighborhoods.

The Homs region has been the site of intense government shelling for more than a week but activists say the city was quiet Saturday.

The U.N. estimates that more than 9,000 people have been killed in Syria's more than year-long crackdown on dissent.