UN Security Council has postponed till tomorrow a vote on a resolution on Syria amid efforts to get Russia and key Western nations to agree on measures required to end the violence and bloodshed in the troubled Arab nation.

The 15-nation Council was scheduled to vote on the Syrian resolution later today.

However, UN-Arab League envoy Kofi Annan requested the Council to postpone voting on the resolution, which threatens to impose sanctions against President Bashar Al Assad's regime if it fails to take action to curb the escalating violence that has killed thousands.

"A possible vote has been postponed until tomorrow," Russia's UN Ambassador Vitaly Churkin told reporters.

The resolution on Syria which has been proposed by Britain, France, Germany and the US seeks to extend the UN observer mission in the country for 45 days.

The resolution is tied to Chapter 7 of the UN Charter, which would allow the Council to authorize diplomatic and economic sanctions as well as military intervention.

Russia has said it will block the resolution as it does not agree to it being tied with the Chapter 7 provisions.

Russia and China have in the past vetoed two UN Security Council resolutions on Syria which were aimed to pressure Assad to halt the violence.

Meanwhile, a suicide bomb attack today killed Syrian defense minister Daoud Rajha, Assad's brother-in-law Asef Shawkat, who was the deputy chief of staff of the Syrian military, and Hassan Turkmani, former minister of defense and military adviser to the Vice President.

The UN estimates that more than 10,000 people have been killed in Syria and tens of thousands displaced.

The mandate of the UN Supervision Mission in Syria (UNSMIS) – which recently suspended its regular patrols due to the escalating violence on the ground – ends on July 20, with Council members expected to decide on its future before then.

The Council established UNSMIS in April to monitor the cessation of violence in Syria, as well as monitor and support the full implementation of a six-point peace plan.

Earlier in the week, UN Secretary-General Ban Ki-moon spoke with Russian Foreign Minister Sergei Lavrov by telephone and discussed the "imperative need" for an immediate halt to the violence in Syria.

Annan, who was in Moscow on earlier this week, said he had a "very good" discussion with Russian President Valdimir Putin, focusing on what measures need to be taken to end the violence and the killing in Syria and how to proceed with a political transition there.

The Joint Special Envoy has previously noted the importance of a united Council on the Syrian crisis, saying that "if the Council speaks with one voice, that voice is much more powerful than when it is divided."