With violence reaching new heights in Syria, the United Nations Security Council unanimously approved a 30-day extension of the monitor mission there on Friday, throwing what amounted to a thin lifeline to Kofi Annan, the special envoy in the Syrian conflict, to save his paralyzed peace plan from total irrelevance.

The 15-to-0 vote came only a few hours before the 300-member mission’s authorization was to expire. A failure to act would have forced the monitors into a hasty withdrawal from Syria, just as deadly mayhem, rebel advances and refugee flows from the 17-month-old uprising against the government of President Bashar al-Assad appeared to be accelerating.

Although the work of the monitors has been suspended for more than a month because of the violence and the disregard for Mr. Annan’s plan by both Mr. Assad’s government and his armed opponents, diplomats feared that scrapping the effort entirely would have sent a message of failure at precisely the wrong moment.

“We believe it is the right thing to do, to give a final chance for the mission to fulfill its function,” Britain’s United Nations ambassador, Sir Mark Lyall Grant, told reporters after offering the resolution that was approved.

The Council extended the mission “for a final period of 30 days,” essentially allowing for an orderly departure. But the resolution left open the possibility of a further renewal if two conditions were met: a halt to the Syrian military’s use of heavy weapons, as promised in Mr. Annan’s plan, and a reduction in violence to a level that would allow the unarmed monitors to resume their work. The basic purpose of the monitor mission is to oversee the carrying out of Mr. Annan’s plan.

Sir Mark and other ambassadors declined to speculate on what appeared to be a rapidly changing picture on the ground in Syria, where activist groups said more than 300 people died in clashes on Thursday and at least 140 on Friday and the United Nations refugee agency reported an enormous surge of people fleeing the country.

Refugee officials in Geneva reported a conspicuous increase in cars departing Damascus, the capital, which had been relatively insulated from the insurgency against Mr. Assad until this week, when rebels of the Free Syrian Army took the fight to neighborhoods in earshot of the presidential palace.

Then, in the most potent strike on the government since the uprising began, a bomb attack killed three of Mr. Assad’s top security officials on Wednesday at one of the government’s most secure locations in the capital. A fourth victim, Lt. Gen. Hisham Ikhtiar, the head of National Security, one of the government’s intelligence agencies, died of his wounds on Friday, Syria’s state television announced.

The public funeral for the first three victims, including Asef Shawkat, President Assad’s brother-in-law and a long-feared security chief, was held Friday in a military ceremony on Qassioun Mountain, overlooking Damascus, state television said. The two top figures officiating were Farouk al-Sharaa, a vice president largely kept out of view since he was singled out by outside powers last year as a possible transitional leader, and Gen. Fahd Jassem al-Freij, who was named minister of defense on Wednesday, immediately after his predecessor died in the bombing.

Mr. Assad and his brother, Maher, the commander of the country’s most elite military forces, did not attend.

The Security Council’s unanimity on extending the monitor mission contrasted with the acrimonious discord in the Council chambers the day before, when Russia and China vetoed a Western-backed British resolution that would have threatened Mr. Assad’s government with economic sanctions under Chapter 7 of the United Nations Charter if he did not comply with the peace plan.

Russia and China have consistently opposed invoking Chapter 7, which can also authorize military intervention to enforce the Council’s will, as an unwarranted intrusion into Syria’s domestic affairs. Western diplomats expressed outrage at the veto and accused Russia and China of protecting Mr. Assad despite his government’s record of brutality.

The Russians and Chinese countered that acts of brutality have been committed by both sides. Russia’s United Nations ambassador, Vitaly I. Churkin, further accused Western nations of concealing what he called their true motive: deposing Mr. Assad in order to deprive Iran of its only remaining Middle East ally.

The Council’s unanimity on Friday barely masked Western anger from the veto 24 hours earlier. Susan E. Rice, the American ambassador, said the Council’s decision to extend the mission for 30 days “was not the resolution the United States had hoped to adopt in the first instance.”

Rather than emphasizing the monitoring mission’s extension as a final opportunity for Mr. Annan’s plan, Ms. Rice described it as a way to allow the monitors “to withdraw safely.” Her description did not sit well with Mr. Churkin.

“I was somewhat surprised to hear Ambassador Rice’s description,” he told reporters later. “This is not about withdrawal.”

But there was no sign that the antagonists in Syria were interested in accepting Mr. Annan’s plan. Iraq was reported to have thrown up blast walls to seal its main border crossing with Syria, Abu Kamal, after rebel forces took control of all four crossings into Iraq and one into Turkey a day earlier.

The government’s accounts of fighting Friday focused on what state television called the valiant rescue of the Midan neighborhood in Damascus from rebel control after days of combat. “Our heroic forces have completely cleansed the Midan area of the terrorist mercenaries and restored security,” state television reported, using the government’s standard label for the rebel forces. It broadcast pictures of bodies of rebels lying in blood, flies buzzing around them.

“We are not ‘armed gangs or terrorist groups,’ ” said Abu Rami, 25, one of the rebel fighters abandoning Midan. “We are a popular armed force and ordinary people support us. If we were not hosted by the people, we could not fight in these districts.”

In the western Damascus neighborhood of Mezze, opposition activists reported helicopters firing heavy machine guns and tanks shelling buildings. In the northern suburb of Qaboun, Syrian soldiers and shabiha, pro-Assad militiamen, joined in teams to chase Free Syrian Army groups.

“The soldiers are moving around in tanks and armored vehicles — they cannot walk because they fear the Free Syrian Army,” said Abu Bassam, a 60-year-old resident who accused the government forces of looting after most residents had fled. The electricity had been cut off since Tuesday, he said, and the area bombed repeatedly from helicopters.

“The F.S.A. controls the land, and the regime’s helicopters own the sky,” he said.

Reporting was contributed by Neil MacFarquhar and Dalal Mawad from Masnaa, Lebanon; Hwaida Saad from Beirut, Lebanon; Alan Cowell from Paris; Nick Cumming-Bruce from Geneva; Duraid Adnan from Baghdad; and an employee of The New York Times from Damascus, Syria. (Copyright 2012 The New York Times Company 07/21/12)