The Syrian government has agreed to immediately begin halting the use of heavy weapons in residential areas and to withdraw its forces from population centers by April 10, envoy Kofi Annan told the U.N. Security Council on Monday.

The latest Syrian commitment, made by Syrian Foreign Minister Walid al-Moualem in a letter to Annan on Sunday, came amid reports that government forces continued to bombard targets in the city of Homs. Some U.N. diplomats voiced skepticism about Syria’s pledge, saying the government has consistently reneged on previous commitments.

“We have seen over the course of the last months promises made and promise broken,” said Susan E. Rice, the U.S. ambassador to the United Nations. “Past experience would lead us to be skeptical and to worry that over the next several days that, rather than a diminution of violence, we might yet again see an escalation of the violence.”

Still, Rice said the 15-nation Security Council would grant Annan additional time to test Syria’s pledge to rein in its forces and would consider his proposal to pull together a U.N. monitoring mission to ensure compliance in a possible cease-fire.

“In general, the council members expressed a willingness to consider Mr. Annan’s plan for a monitoring mission,” said Rice, who holds the council’s rotating presidency and who briefed reporters on the plan.

Annan, a former U.N. secretary general who is serving as the joint Arab League-U.N. envoy for Syria, presented the council with a detailed, closed-door briefing on his efforts to implement a six-point plan to end the violence in Syria.

He told the council that he had underscored the “urgency” of the crisis with Syria’s leadership and that he had “pressed the government to cease troop movements, cease the use of heavy weapons and pull out of population centers,” Rice told reporters after the meeting.

Annan told the council that his deputy, Nasser al-Kidwa, the former Palestinian envoy to the United Nations, had urged opposition groups inside Syria “to cease their operations within 48 hours of a compete cessation of government hostilities.”

Annan also said he is awaiting a response from the Syrian government on other elements of the peace plan, including a request to provide access to humanitarian aid workers and journalists, to observe a daily pause in the fighting and to participate in political talks with the opposition.

After the Security Council meeting, Syria’s U.N. envoy, Bashar al-Jaafari, said his government is “committed to the success” of Annan’s mission but that opposition forces would also have to put down their arms.

“We are expecting Mr. Kofi Annan and some parties in the Security Council to get the same kind of commitment from the other parties,” Jaafari said. “The plan wouldn’t be successful unless everybody is committed.”

Jaafari lashed out at the United States, Turkey, Saudi Arabia and other governments that met in Istanbul over the weekend and committed to step up support for the armed opposition in Syria. The meeting of the “Friends of Syria” resulted in a pledge from Arab nations to provide $100 million to pay salaries for opposition fighters and a commitment from the Obama administration to provide “non-lethal” assistance, including communications equipment and night goggles, to help the rebels move about Syria undetected.

“This is a parallel track set up by the enemies of Syria to compete with Kofi Annan’s mission . . . maybe to undermine the mission,” Jaafari said. He said that the United States and other governments sending money and other supplies to the armed opposition “should be put in the confessional seat in the Security Council, and ask them what they are doing. . . . This is a violation and a declaration of war against the sovereignty of Syria.”