Hundreds of youths blocked roads leading to the city's main residential neighborhoods with garbage containers, wood and metal to try to prevent a possible advance. Inhabitants joined in their shouts of "God is greatest," from balconies and rooftops, residents said.

Tanks and armored vehicles moved overnight to the edges of the city, including 30 seen near a flyover on a road leading west, they said, a day after hundreds of troops and security police entered Hama at dawn in buses, killing at least three people in raids on main neighborhoods.

Hama, scene of a bloody crackdown by Assad's father nearly 30 years ago, has witnessed some of the biggest demonstrations and highest death tolls in Syria's 14-week uprising, inspired by revolts across the Arab world.

The two countries have opposed a United Nations Security Council resolution proposed by the West against Syria, helping Assad withstand mounting international isolation.