Syrian opposition activists say government tanks have staged outside the central city of Hama, a day after soldiers raided homes and arrested at least 20 people there.

The activists say residents have set fires and placed debris in the streets to try to block troops from entering Hama amid the on-going crackdown on protests.

Hama is one of the centers of opposition to President Bashar al-Assad's 11-year autocratic rule, and was the site of an anti-Assad rally on Friday that drew hundreds of thousands of protesters. Oppositon activists say three people, including a young boy, were killed by government troops on the outskirts of the city Monday.

Rights groups say at least 1,300 civilians have been killed by Syrian security forces since mid-March. The Syrian government says terrorists and Islamist militants have killed hundreds of security personnel in the same period.