UN Secretary-General Ban Ki-moon and the Security Council Friday expressed "grave concern" over the deteriorating situation in Syria.

"All violence is unacceptable and must stop," Ban said in a statement.

The Syrian opposition blamed President Bashar Assad's regime for the Friday bombing in the capital Damascus. A bomber blew himself up at a traffic intersection, near an elementary school.

The UN Security Council in a press statement called the attack a "heinous act" and expressed condolences to the victims.

The Security Council is to once more take up the issue of sanctions against Syria on Tuesday. But the United States was not optimistic that it would produce any results.

China and Russia, two of the five veto-wielding council members, have opposed a resolution to condemn the violence. But the UN General Assembly voted overwhelmingly in December to condemn the country's human rights abuses.

In Washington, U.S. State Department Victoria Nuland indicated that a resolution was not yet in sight.

"I think this is going to be the next stage in consultations," she told reporters. "I'm not sure that we're expecting to finalize anything on Tuesday."

According to UN estimates, more than 6,000 people have died in the clashes between advocates for reform and the Syrian government that began in January 2011.