A top UN official says that Secretary-General Ban Ki-moon is "gravely concerned" about the rising death toll in Syria.
Assistant Secretary-General Oscar Fernandez Taranco told the Security Council that Ban wanted the 15-nation body to unite to apply "sustained pressure" on the Syrian government to apply the six-point peace plan of UN-Arab League envoy Kofi Annan.
The plan was never implemented by the two sides.
The United States has recently criticized Russia for blocking UN resolutions threatening tough sanctions against the regime of President Bashar al-Assad, as well as for continuing arms sales to Damascus.
Ban said last month that at least 10,000 people had been killed in the Syria conflict, but UN sources say the actual death toll is likely much higher -- probably around 14,000.
Taranco told the council on June 19 that the situation was "particularly alarming" in the rebel city of Homs, where human rights monitors say thousands of people have been trapped in a bombardment by government forces.
Taranco was speaking ahead of a UN Security Council meeting on the escalating conflict.
Monitoring Mission Suspended
Major General Robert Mood, head of the UN Supervision Mission in Syria (UNSMIS), is to brief the Security Council in a closed meeting.
The briefing comes after the UN mission on June 16 suspended patrols by its 300 unarmed observers, saying the escalating violence between Assad's forces and rebels was making the mission too dangerous.
The UN observers were sent to Syria in April to monitor the implementation of the Annan peace plan.
Russia has supported the UN observer mission, and has repeatedly called for all the Syrian parties to implement the UN-Arab League peace plan.
But Moscow has vowed to oppose any foreign intervention in the conflict, saying a resolution must be determined by Syrians only.
Analysts say the continuing bloodshed in Syria has raised doubts about the viability of the UN observer mission, whose three-month mandate expires on July 20, and it is unclear whether the Security Council will renew the observers' mission.
In a joint statement issued on the sidelines of the G20 summit in Mexico, U.S. President Barack Obama and Russian President Vladimir Putin called for "an immediate cessation of all violence" in Syria.
However, there was no sign the two UN Security Council powers had agreed on a plan aimed at ending the conflict.
Obama told reporters after the meeting that he and Putin agreed "that a political process has to be created to prevent civil war and the kind of horrific deaths that we've seen over the last several weeks.
Obama said he and his Russian counterpart had "pledged to work with other international actors, including the United Nations, Kofi Annan, and all interested parties, in trying to find a resolution to this problem."
Putin said they had found "many common points on all the issues."
With reporting by AFP, AP, and Reuters