International envoy Kofi Annan has asked the U.N. Security Council to delay a vote on a new resolution on Syria scheduled for Wednesday, after a bomb blast killed at least three top Syrian officials in Damascus.

Earlier in the day, U.S. Defense Secretary Leon Panetta said the bombing is evidence that the situation in Syria is “rapidly spinning out of control.” He called on the international community to exert “maximum pressure” on Syrian President Bashar al-Assad to step down.

In Moscow, Russian defense minister Sergei Lavrov said Moscow cannot approve a U.N. resolution imposing sanctions on Syria. Russia has produced an alternate resolution that does not include sanctions.