File photo - A Syrian injured man, who lost his leg from the Syrian forces shelling at Baba Amr neighborhood in Homs Province in February, uses a walker as he does his daily walking exercise at a hospital, in the northern port city of Tripoli, Lebanon.

United Nations - Time is running out for U.N.-backed peace efforts in Syria as the escalation of violence in the country's 15-month conflict drives the death toll higher and sparks more human rights abuses, a senior U.N. official said on Tuesday.

The remarks came after Syrian security forces pounded opposition areas across the country on Monday, activists said, adding that at least 23 people had been killed in clashes they say have become worse since U.N. observers suspended their activities over the weekend.

“The Secretary-General (Ban Ki-moon) remains gravely concerned about the intensification of violence and rising death toll, as well as continued human rights abuses and unmet humanitarian needs,” said Oscar Fernandez-Taranco, the U.N. assistant secretary-general for political affairs.

Ban said last month that at least 10,000 people have been killed in the Syria conflict, but U.N. diplomats say the actual number is likely much higher.

“The situation in Homs is particularly alarming,” Fernandez-Taranco told the 15-nation Security Council during a discussion on the Middle East. “The tragic human suffering from the escalating conflict calls for urgent and concerted efforts to avoid a full-scale civil war.”

The head of the U.N. peacekeeping department, Herve Ladsous, said last week that Syria was already in the throes of an all-out civil war.

Days after Ladsous made that announcement in an interview with Reuters and AFP, the chief U.N. monitor in Syria, General Robert Mood, announced that the monitoring mission in Syria had suspended operations, in the clearest sign yet that a peace plan brokered by mediator Kofi Annan has collapsed.

Mood will brief the Security Council in person later on Tuesday about the escalation of violence and his decision to suspend the activities of the U.N. monitoring mission.

“Time is running out,” Fernandez-Taranco said. “The government of Syria bears the prime responsibility to change course and fully implement (Annan's) six-point plan. Shelling and firing against population centers by government forces including tanks and helicopters, must stop immediately.”

He added that the opposition must also stop fighting.

Syria said on Tuesday it was trying to evacuate civilians from the city of Homs and blamed rebel fighters for obstructing efforts to get people out safely. Damascus blames “armed groups” and foreign-backed “terrorists” for the conflict.

Opposition activists say the army has intensified shelling of residential districts in the city of Homs, center of the revolt against President Bashar al-Assad, and General Mood said he was worried about civilians trapped there.

Fernandez-Taranco reiterated U.N. chief Ban's and his predecessor Annan's calls for the Security Council, which remains deadlocked on the issue of Syria, to put “unified and sustained pressure to demand compliance in fully with the six-point plan.”

“Otherwise we may be reaching the day when it will be too late to stop the crisis from spinning out of control,” he said.

U.S. and European council members have called for the 15-nation body to impose sanctions on Damascus but Syria's staunch ally and arms-supplier Russia, along with fellow veto power China, have repeatedly rejected the idea. - Reuters