Syrian rights activists say at least 12 people have been killed and many more wounded in a new bombardment by Syrian forces on the flashpoint city of Homs.

Arabic satellite television stations broadcast images from Homs Monday that showed smoke billowing into the sky from buildings damaged in the attack. Several parts of the city were hit.

There was no independent confirmation of the casualties as Syria restricts independent reporting in the country.

The attack comes several days after activists reported what they called a massacre in Homs, saying at least 200 people died in a government bombardment late Friday into Saturday, in what appeared to be one of the deadliest incidents of the 11-month revolt.

Homs has become a focal point of opposition resistance to the government of Syrian President Bashar al-Assad.

On Sunday, activists said fighting between pro-Assad troops and loosely-organized rebels killed at least 56 people, about half of them civilians.

Also Sunday, Russia and China defended their veto of a U.N. Security Council resolution that would have endorsed an Arab League plan for Mr. Assad to transfer power to help end Syria's unrest.

Russia said it vetoed the Western and Arab-backed resolution Saturday because of what it viewed as “ultimatum-like” demands for the removal of Mr. Assad, Moscow's only military ally in the Middle East.

China said it vetoed the resolution to oppose what it perceives as an effort to promote “regime change” in Syria through “external force,” in violation of international norms.

U.S. Secretary of State Hillary Clinton denounced the double veto as a “travesty.” She said the United States will work with its allies outside the United Nations to tighten “regional and national” sanctions on Syria.

Syria's opposition uprising against Mr. Assad's autocratic rule has escalated in recent months into open conflict between rebels and pro-Assad forces. Last month, the United Nations estimated the death toll from the unrest at 5,400 before it stopped updating the figure because of difficulties in obtaining information.