Syria's main opposition coalition has called for emergency meetings of the United Nations Security Council and the Arab League to discuss the intensifying violence in the north-west of the country.
The Syrian National Council, which is based outside Syria, says about 250 people have been killed since Monday.
A human rights group has accused Syria of carrying out an organised massacre in Idlib province.
Arab League monitors are due in Syria on Thursday.
Foreign journalists are not allowed to report freely in Syria so details are hard to verify.
