UNITED NATIONS: UN chief Ban Ki-moon and international envoy Kofi Annan called on the UN Security Council to take strong action on the Syria conflict ahead of a vote Thursday on a western-backed resolution calling for sanctions.

Russia and China are expected to veto the resolution at the 15-nation council despite mounting global concern over Syria after a Damascus bomb attack in which three close associates of President Bashar al-Assad were killed.

Ban said there was an “extreme urgency” for action to make government and opposition forces halt the violence.

Annan, the UN-Arab League envoy, said the council must take “decisive” action on the conflict after he persuaded the major powers to postpone the vote originally set for on Wednesday.

“The deteriorating situation in Syria underscores the extreme urgency for all sides to stop armed violence in all its forms, implement the six point plan and move swiftly towards a political dialogue,” Ban said in a statement.

Ban “strongly condemns” the Damascus bomb attack in which Defense Minister General Daoud Rajha and two other top members of Assad's entourage were killed, said the statement released by his office.

He expressed concern about the use of “heavy weapons by Syrian security forces” and urged the Security Council “to shoulder its responsibility and take collective and effective action on the basis of UN Charter obligations and in view of the seriousness of the situation.”

Annan intervened just ahead of a scheduled vote on the western resolution Wednesday to get it delayed. But with no new diplomatic proposals emerging, a new vote was called for Thursday.

The UN-Arab League envoy “urged members of the Security Council to unite and take concerted and strong action that would help stem the bloodshed in Syria and build momentum for a political transition,” said his spokesman Ahmad Fawzi.

Annan believes the latest violence “only underscores the urgency of decisive council action.”But Russia maintained a threat to veto any resolution under Chapter VII of the UN Charter.

Russia's President Vladimir Putin and US President Barack Obama spoke by telephone, but failed to overcome differences over the conflict.

“We cannot accept Chapter VII and the section about sanctions,” Russia's Foreign Minister Sergei Lavrov said in Moscow on Wednesday.

Russia and China, using their powers as permanent council members, have twice vetoed previous resolutions hinting at sanctions against Damascus.

The British resolution, backed by the United States, France, Germany and Portugal, calls for non-military sanctions under Chapter VII if Assad does not withdraw heavy weapons from Syrian cities in 10 days.

“We will be voting tomorrow morning,” said Britain's UN Ambassador Mark Lyall Grant.

“We have very clearly said to our Russian and Chinese friends, we are ready to negotiate,” said France's UN Ambassador Gerard Araud.

“It is a Chapter VII resolution with a threat of sanctions. We consider the situation is serious enough in Damascus and in Syria that we move towards this goal,” he told reporters.

“We want to give diplomacy a chance but there has to be meaningful engagement on the side of Russia and China with our resolution,” Germany's UN envoy Peter Wittig told reporters.

The mandate of the UN Supervision Mission in Syria (UNSMIS) ends on Friday and without a resolution, the UN may have to hurriedly withdraw the nearly 300 unarmed observers now in Damascus.

More than 17,000 people have been killed since an uprising against Assad began 16 months ago, activists say.