At least four people were killed on Monday as Syrian security forces carried out raids in and around the flashpoint central city of Homs, rights and activist groups reported.
"Two people were killed and seven others were wounded in Homs while two others died and eight were wounded in [nearby] Qusair by gunfire during raids on Monday morning by the army and security forces," said the Syrian Observatory for Human Rights.
The military also raided the towns of Karnaz, Latalmleh and Kafar Nabude in the central province of Hama, the Britain-based Observatory said in a statement received in Nicosia.
Dozens of military vehicles carried troops into northern Idlib province, where heavy machinegun fire was heard in the village of Ehseen and telephone lines were cut, it added.
The Local Coordination Committees said that as many as five people, including a Saudi national, were killed in Homs after 20 armoured vehicles entered the neighbourhood of Al-Bayada.
Eight people were wounded by "random gunfire" and rocket-propelled grenades fired at a building, the LCC said in a separate statement received by AFP.
The LCC, an opposition umbrella group that organises activists on the ground, said that a similar security operation was conducted in the city of Hama, farther to the north.
The latest bloodshed came after Syria's Foreign Minister Walid Muallem on Sunday brushed off the threat of a civil war and looming Arab League sanctions.
At least 24 more people were reported to have been killed at the weekend, adding to the UN figure of the more than 3,500 deaths since mid-March in the Syrian crackdown on protests.