Syrian President Bashar al-Assad appears to have disappeared from Damascus after his top security staff was killed in a suicide bombing. There has been no statement from the president, nor any sign of him since the attack Wednesday on the central government headquarters.

Clashes erupted Thursday near government headquarters in Damascus as opposition forces attacked loyalist troops, vowing to “liberate” the capital, activists and residents said.

One person was reported killed in the fighting by late morning in a neighborhood next to the Council of Ministers, a huge complex, and a Damascus University campus, sources said.

Assad’s brother-in-law, his defense minister and a top general were all killed Wednesday at a meeting of defense and security chiefs.

A security source said the bomber, who struck the security headquarters itself, was a bodyguard for Assad’s own inner circle.

The United Nations Security Council, which had planned to meet Wednesday, delayed a vote on a Syria resolution until Thursday.

U.N. Secretary-General Ban Ki-moon said Thursday he was alarmed by the intensifying violence in Syria and that he “strongly condemns” the bombing in Damascus that killed  top defense and security chiefs.

Ban “is also gravely concerned about reports of the continued use of heavy weapons by the Syrian security forces, including in the Damascus area, against civilians, despite repeated government assurances that such weapons would be withdrawn,” the United Nations said in an emailed statement.

Ban, who is on a three-day visit to China, urged members of the Security Council to take collective and effective action in view of the escalating situation in Syria.

“Time is of the essence,” Ban said. “The Syrian people have suffered for too long. The bloodshed must end now.”