The Local Coordination Committees of Syria said security and government forces entered the Tal Refaat neighborhood of Aleppo, the country's economic center, CNN reported.
The rights group said al-Rastan was hit Tuesday by army personnel armed with "heavy machine guns mounted on tanks," injuring 20 people, seven seriously.
Since March, demonstrators have demanded democratic reforms and Assad's ouster. Some human rights groups said nearly 3,000 people have died in the government crackdown, but the figures can't be independently verified because Syria has restricted foreign journalists' access to many parts of the country.
The Syrian government said it wants to initiate reforms, but has been protecting citizens from terror groups and thugs.
At the United Nations, Syrian Foreign Minister Walid Moallem blamed "foreign incitement" for the country's ills, fueled by U.S. and European sanctions.
"This course cannot in any way be reconciled with pronouncements about concern for the interests, security and rights of the Syrian people," Moallem said. "It further runs counter to the basic principles of human rights in defense of which these states base their interference in our internal affairs."
The government-run Syrian Arab News Agency reported Monday authorities found Israeli weapons, explosives and stolen military uniforms in Homs, as well as uncovering weapons and military supplies at a house in Naseeb in Daraa province.