Updated

The Security Council unanimously approved a resolution Saturday expanding the number of U.N. cease-fire observers in Syria from 30 to 300 and demanding an immediate halt to the violence that has been escalating since the government and opposition agreed to end hostilities over a week ago.

The resolution gives Secretary-General Ban Ki-moon authority to decide when to deploy the additional observers, based on developments on the ground including "the consolidation of the cease-fire." Ban accused Syrian President Bashar Assad on Thursday of failing to honor the cease-fire, expressing dismay that increased violence is claiming more lives.

The resolution merged rival Russian and European texts and dropped a European threat of non-military sanctions against Syria if it fails to withdraw troops and heavy weapons from towns and cities. Instead, it uses language from the resolution adopted last Saturday authorizing deployment of the 30-strong advance team of observers which expresses the council's intention to assess implementation of the new resolution "and to consider further steps."

Russia's U.N. Ambassador Vitaly Churkin told the council after Saturday's vote that the resolution is "of fundamental importance to push forward the peace process in Syria" and to support the six-point peace plan negotiated by international envoy Kofi Annan.

Britain's U.N. Ambassador Mark Lyall Grant said the expanded observer mission and Annan's proposal "represents the last opportunity to secure a solution to the crisis in Syria."

"It is an unprecedented step to deploy unarmed U.N. personnel into such a dangerous environment," Lyall Grant said. "It is fraught with risk. The mission will fail in its task if the regime continues to violate its commitments and obstructs the work of the mission."

The resolution establishes a United Nations Supervision Mission in Syria, to be known as UNSMIS, "comprising an initial deployment of up to 300 unarmed military observers as well as an appropriate civilian component" for an initial period of 90 days.

The Russians had called for a limited civilian component, while the Europeans wanted to spell out the skills required of the civilians, including political, human rights, civil affairs and public security.

The key difference in the original texts was whether there should be any conditions for deployment of the expanded force.

The Europeans wanted the secretary-general to determine "to his satisfaction" that Syria has implemented its pledge to send troops and heavy weapons back to their barracks. The Russian draft had no conditions.

The compromise language in the resolution says the expanded mission "shall be deployed expeditiously subject to assessment by the secretary-general of relevant developments on the ground, including the consolidation of the cessation of violence."

France's U.N. Ambassador Gerard Araud said Friday night that the Security Council wants to send the observers as quickly as possible but "at the same time, we have to take into account the danger for the observers -- so that's the reason why the secretary-general will have to assess the situation on the ground."

"It's a new type of mission," Araud explained to reporters. "It's a first time that the U.N. is sending in a war zone observers, because there is still fighting ... there is still violence."

He said it's important to have civilian observers as well who can see, for example, what's happening with the detainees. He said the size and skills of the civilian contingent is always decided by the secretary-general.

The issue of the use of helicopters and aircraft by the U.N. mission will likely dominate discussions in the coming days.

The initial Russian draft resolution made no mention of helicopters but the European version underlined the need for the Syrian government "to agree rapidly" with the U.N. on "the independent use of air assets" by the expanded force.

The final text underlines "the need for the Syrian government and the United Nations to agree rapidly on appropriate air transportation assets for UNSMIS."

Unlike most resolutions that call for reports to the Security Council in 30 days, the resolution adopted Saturday calls for reports every 15 days.

Araud said this will enable the council to react "if things are going bad," not only politically and on the ground, but "we are also in charge of the lives of our observers."

Seven of the advance observers are already on the ground, another two will arrive Monday, and the U.N. hopes to have rest of the advance team of 30 in Syria next week, Annan's spokesman Ahmad Fawzi told The Associated Press in Geneva.

Members of the advance team are being borrowed from U.N. missions in the region so they can deploy quickly, he said. The U.N. said the observers already in Syria come from Morocco, Brazil, Belgium, Switzerland, Russia and Norway.

The preliminary agreement between Syria and the United Nations on the deployment of U.N. observers says they will have freedom to go anywhere in the country by foot or by car, take pictures, and use technical equipment to monitor compliance with the cease-fire engineered by Annan.

The observers, who report to Annan daily, will have freedom to install temporary observation posts in cities and towns, to monitor military convoys approaching population centers, to investigate any potential violation, and to access detention centers and medical centers in coordination with the International Committee of the Red Cross and Syrian authorities, the agreement says.