Syrian Activists say Government Troops Have Attacked Opposition Hubs

This image made from amateur video and released by the Syria Media Center purports to black smoking rising from buildings in Homs, Syria, March 20, 2012. (AP/Syria Media Center)

This image made from amateur video and released by Ugarit News purports to show a Syrian military tank in Homs. (AP/Ugarit)

Syrian army soldiers raid a building as they search for Syrian rebels in a suburb of Damascus, Syria. (AP)

Syrian army soldiers look through a hole in a building as they search for Syrian rebels in a suburb of Damascus. (AP)

A man reacts at a funeral of the victims of a bombing attack in Damascus, Syria, March 18, 2012. (AP)

Men bow in prayer at a funeral of the victims of a bombing in Damascus, Syria. (AP)

Syrian military carry coffins of the victims killed in a bombing attack in Damascus, Syria. (AP)

Thousands of people wave Syrian flags during a silent march in front of a damaged government building on al-Qassa street in Damascus in memory of people who were killed in explosions one day earlier. (AP)

This photo released by the Syrian official news agency shows a building damaged in a blast in Aleppo, Syria, March 18, 2012. (AP/SANA)

A Syrian rebel runs with his AK-47 towards a Syrian army checkpoint in a suburb of Damascus, Syria, on March 17, 2012. (AP)