Syria's regime has launched a heavy and widespread series of air strikes on seven cities or regions which killed at least 20 people, activists said.
After weeks of rebel gains in the south, the government urged them to surrender their arms, warning in text messages that the army is "coming to get you". State television said the primary goal of the air strikes was to "recapture areas taken by the terrorists" - the term the regime uses to refer to opposition fighters in the civil war.
Rebels trying to topple president Bashar Assad have been making gains, especially in the south near the border with Jordan. They have seized military bases and towns in the strategically important region between Damascus and the border with Jordan, 100 miles away.
Last week, they looked poised to take over the area along the Jordanian border, which could be used to try to stage an attack on Damascus, Assad's seat of power. Some rebel factions are also receiving heavier flows of weapons through Jordan as well as training there by the US and other countries.
The rebels already controlled large areas of northern Syria, and captured their first provincial capital - the north-eastern city of Raqqa - last month.
The Britain-based Syrian Observatory for Human Rights said Sunday's air strikes targeted the northern city of Aleppo, the central cities of Homs and Hama and the city of Idlib in the north near the Turkish border. The western Mediterranean city of Latakia, the eastern province of Deir el-Zour and the suburbs of Damascus were also targeted.
Regime fighter jets pounded villages in rebel-held areas in Latakia province before. But they do not frequently hit the city of the same name that is mostly populated with Syrian minority communities including many members of the Alawite sect, an offshoot of Shiite Islam that Assad and his family belong to.
The rebels and opposition supporters are mostly Sunni Muslims, a majority in Syria.
Anti-government activists in Aleppo posted videos online, showing the aftermath of an air strike on Saturday on what they said was Sukkary district in the northern city. Dozens of residents are standing on piles of rubble in front of a row of residential buildings, looking in disbelief at the front of the building that was blown off when a missile slammed into it.
In another video, men are seen helping a woman climb down from a balcony of the second floor of a building that has partially collapsed after a missile strike. The videos appear consistent with reports from the area.