Syrian army units stormed into the city of Banias with tanks overnight, attacking the districts that had defied the rule of President Bashar al-Assad.
Human rights activists say the units entered the city on the night of May 6-May 7 from three directions, and that security forces have killed at least three people.
Electricity and communications were cut as the tanks entered the southern sector of the city on the Mediterranean coast, the bastion of the protesters.
Meanwhile, the White House has warned that the United States and its international partners will take what it calls "additional steps" against the Syrian regime unless its security forces stop killing and harassing pro-reform protesters.
The statement was released after at least 26 people were reported killed by Syrian security forces on May 6.
White House press secretary Jay Carney said in a statement that "the United States believes that Syria's deplorable actions toward its people warrant a strong international response."
It said that unless there is change, the U.S. and its partners would take further measures to make clear their "strong opposition to the Syrian government's treatment of its people."
Human rights groups say more than 580 civilians have been killed by security forces and thousands of people injured or arrested during the past seven weeks of demonstrations against the Syrian regime.
compiled from agency reports