Heavy gunfire erupted as Syrian troops backed by tanks entered several towns in the flashpoint central province of Homs on Monday, activists said.
"The community of Hula is under siege ... The army is carrying out raids and arrests under the cover of heavy gunfire," the Syrian Observatory for Human Rights said.
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Another rights monitoring group said "a large number of tanks entered Hula this morning."
"Security agents encircled all the entrances to into Hula and they started shooting to terrify local residents. Then the army went in to make raids and arrests," said the Observatory.
It said pro-regime militiamen and security agents were deployed on all roads and in villages around Hula to erase anti-government graffiti from the walls.
The Homs operation came a day after gunboats joined in a pounding of the port city of Latakia that killed 26 people, in the first attack from the sea since an anti-regime revolt erupted in March, according to activists.