U.S. Secretary of State Hillary Clinton on Monday denounced the growing violence in Syria, calling on the UN Security Council to act.

"The United States condemns in the strongest possible terms the escalation of the Syrian regime's violent and brutal attacks on its own people," the top U.S. envoy said in a written statement.

She accused the Syrian government of shelling civilian areas with mortars and tank fire and bringing down whole buildings on top of their occupants, saying that hundreds of civilians have been killed as a result in the past few days.

The Arab League decided to suspend its observer mission in Syria on Saturday, citing the deteriorating situation and the continuous use of violence in the country.

Clinton charged that the Syrian government has failed to meet its commitments to the Arab League to halt its acts of violence, withdraw its military forces from residential areas, allow journalists and monitors to operate freely and release prisoners arrested because of the current unrest.

"The Security Council must act and make clear to the Syrian regime that the world community views its actions as a threat to peace and security," she said. "The violence must end, so that a new period of democratic transition can begin."

Noting that she would attend a Security Council meeting on Syria slated for Tuesday, she said that the international community should send a clear message of support to the Syrian people.

"The longer the Assad regime continues its attacks on the Syrian people and stands in the way of a peaceful transition, the greater the concern that instability will escalate and spill over throughout the region," she added.

Damascus has rejected a new plan suggested last week by the Arab League, calling it "blatant interference" in Syria's internal affairs, as the plan urged Syrian President Bashar al-Assad to delegate power to his first vice president and envisioned the formation of a national unity government within two months.

The UN says at least 5,400 people have been killed in the unrest that began in March, while the Syrian government says more than 2,000 army and security personnel are among those killed in the violence.