AMMAN, Jordan -- After weeks of rebel gains in the south, Syria's regime launched a heavy and widespread series of airstrikes on Sunday that targeted at least seven cities or regions and killed at least 20, activists said.

The government also urged rebels to surrender their arms, warning in cellphone text messages that the army is "coming to get you."

State television said the primary goal of the airstrikes 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 in recent weeks, 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, about 160 kilometres (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 U.S. and other countries.

The rebels already controlled large swaths of northern Syria, and captured their first provincial capital -- the northeastern city of Raqqa -- last month.

The Britain-based Syrian Observatory for Human Rights said Sunday's airstrikes targeted the northern city of Aleppo, the central cities of Homs and Hama and the city of Idlib city in the north near the Turkish border. The western Mediterranean city of Latakia, and the eastern province of Deir el-Zour and the suburbs of the capital 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 on line, showing the aftermath of Saturday's airstrike on what they say is 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 ripped through it.

The videos appear consistent with AP reporting from the area.

The Aleppo strike was the deadliest air raid on Sunday, killing up to 12 people, according to another anti-regime activists group, The Local Coordination Committees.

In the southern city of Daraa, a man was shot and killed by an army sniper, the Observatory said. It added that there was little rebel advancement in the province where opposition forces seized large swaths of land over the past two weeks.

In the outskirts of Damascus, the army pursued rebels in Adra district and raided their base in the neighbourhood of Qarra, the state news agency SANA reported.

It also said the army "demolished two dens with all terrorists and ammunition inside them in al-Khalidiya district in the central province of Homs, killing several terrorists." It provided no other details.