UNITED NATIONS—The U.N. Security Council voted on Saturday to send 300 unarmed U.N. cease-fire observers to Syria as soon as the U.N. secretary-general determines it is safe to do so, as an advance team of seven monitors visited the battered city of Homs for the first time.

The 15-member council unanimously approved the full monitoring mission after a compromise was reached between Russia and the West. Moscow had wanted to deploy the observers immediately while Western powers had demanded that Syrian government forces withdraw from populated areas first, a key element of the U.N.´s six-point peace plan agreed to by the government and the rebels.

Under the resolution adopted, the monitors will only be deployed "expeditiously" if Secretary-General Ban Ki-moon assesses that the cease-fire has been "consolidated."

The monitors could be sent in as soon as this happens for a period of 90 days. But if Mr. Ban determines that the violence hasn´t slowed sufficiently, and if Syrian forces don´t withdraw from towns and cities in 15 days when Mr. Ban must report, the council will "consider further steps as appropriate," the resolution says. What those steps are aren´t spelled out.

Syrian Ambassador Bashar Ja´afri told the council, "They are bragging about tightening these sanctions…but we reject interference in our internal affairs. Mr. Ja´afri blamed the West and its Arab partners for interfering in Syria´s affairs. "Syrians well know these external forces and…do not want any Wahhabi or Salafist factions to penetrate its ranks through some terrorists propagated by Saudi Arabia and Qatar."

The initial Western plan had explicitly called for sanctions against Damascus if in 15 days it didn´t end the violence and withdraw its forces. The Russian draft resolution hadn´t posed any threat of sanctions, which Moscow opposes.

"This mission and the…six-point proposal represents the last opportunity to secure a solution to the crisis in Syria," said British Ambassador Mark Lyall Grant. "A failure of the regime to meet its commitments, or any further attempt to hinder the work of the mission, must be met with robust sanctions by this Council."

Susan Rice, the U.S. ambassador, warned Damascus that if the violence doesn´t stop soon the U.S. would be ready to push for a strong response and it wasn´t willing to wait.

"For the United States, our patience is exhausted," she said. "No one should assume that the United States will agree to renew this mission at the end of 90 days. If there is not a sustained cessation of violence and freedom of movement for U.N. personnel…then we must all conclude that this mission has run its course."

"We will not wait 90 days to pursue measures against the Syrian government if it continues to violate its commitments," Ms. Rice said.

"We are sober about the risks, all the more so given the long record of the Assad regime´s broken promises and disregard for the most basic standards of humanity," Ms. Rice went on. "The deployment of 300 or 3,000 monitors on its own cannot stop the regime from waging its barbaric campaign of violence against the Syrian people. What can bring a halt is continuous pressure on the regime."

Russian Ambassador Vitaly Churkin responded, "Some would like to see the strategy to fail because as we heard, they have other plans. This is very unhelpful."

After blocking earlier attempts to reach Homs, scene of the worst violence in the 13-month uprising against President Bashar al-Assad, U.N. monitors visited the city on Saturday in a rare moment of calm.

Activists however said that the government had only temporarily stopped its shelling to create a false impression for the observers.

The resolution asks Damascus to give the observers unhindered movement and freedom to interview any Syrian without a threat of reappraisal.

The government is to provide the observers´ security, the resolution says.

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

The U.N. and the government were also urged to agree "rapidly" on the monitors´ use of helicopters and planes. Mr. Ban has said the U.N. would find its own aircraft if Syria fails to provide them.

The government is also to allow immediate and unhindered access to humanitarian aid. The resolution condemns "widespread" human rights violations by the Syrian government and "any human rights abuses" by "armed groups." It says that those responsible will be held accountable.

The monitoring mission, to be known as the U.N. Supervision Mission in Syria, or UNSMIS, will also have a civilian staff, including human rights monitors.

"This resolution overcomes Russian attempts to neuter UNSMIS and provides a solid basis for deploying human rights experts to monitor key aspects of the Annan plan, such as protecting civilians, respecting the right to peaceful assembly, and releasing those arbitrarily detained," said Philippe Bolopion, Human Rights Watch´s U.N. director. (Copyright © Dow Jones & Company, Inc.) 04/22/12)