Syrian security forces reportedly detained hundreds of people in a sweep through villages around Jisr al-Shughour on June 13, after President Bashar al-Assad's army reoccupied the rebellious city near the Turkish border.
The army used tanks and helicopters on June 12 to seize Jisr al-Shughour.
Activists say up to 7,000 people have already fled the region around the town, seeking sanctuary in neighboring Turkey.
The government said last week that "armed gangs" killed more than 120 security troops in the town after demonstrations there.
But refugees and rights groups say many of the dead were civilians killed by security forces or soldiers who were shot for refusing to fire on civilians.
Syrian refugees who crossed into Turkey overnight said some soldiers continue to fight against regime loyalists in the area. With foreign correspondents banned from Syria, it was not immediately possible to confirm those claims.
The United Nations meanwhile warned that at least 10,000 Syrians have fled the violence. UN humanitarian affairs spokeswoman Stephanie Bunker said there are at least 5,000 Syrian refugees in Turkey and 5,000 in Lebanon.
Syrian rights groups say 1,300 civilians have been killed since the start of the uprising.
One group, the Syrian Observatory for Human Rights, says more than 300 soldiers and police have also been killed.
The White House said on June 13 that it condemned in the "strongest possible terms" the latest violence by the Syrian government.
UN Secretary-General Ban Ki-moon said he had talked with President Bashar al-Assad and urged him to take "decisive actions to listen to the people."
The move comes against the backdrop of a harsh government crackdown on national protests against Assad's rule that first began in March.
It also comes as international outcry increases over Syria's actions, which reportedly have included the use of helicopter gunships to fire on protesters.
European states have drafted a proposed UN resolution condemning the Syrian authorities' use of force in the crackdown and calling for its end.
International media have been denied access to the country, making developments difficult to track.
compiled from agency reports