Troops and tanks are reported to have swept into the Syrian city of Baniyas, a centre of anti-government protests.
They entered in three places and descended on the Sunni districts of the coastal city, human rights activists told news agencies.
Communications to the city and surrounding areas appear to have been cut making the reports hard to verify.
Rights activists say more than 580 people have been killed in the uprising since mid-March.
However, Syrian rights group Sawasiah told Reuters news agency on Saturday it has the names of at least 800 civilians who have died.
Syrian officials have given a lower death toll, and say half the fatalities have been soldiers and police, killed by “armed terrorist groups”.
At least 26 people were reportedly killed in Homs, Hama and other cities on Friday, in what protesters had vowed would be a “day of defiance”.
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