Army defectors in southern Syria battled loyalist forces backed by tanks in a major armed confrontation Sunday near the Jordanian border, as up to 18 people were killed in nationwide violence.

Residents and activists said government troops from Syria's 12th Armored Brigade stormed the southern town of Busra al-Harir overnight. The British-based Syrian Observatory for Human Rights said three military vehicles were burned in the clashes. The group said similar battles took place Sunday in several other parts of the south.

Reuters quoted local residents as saying defectors had been hiding in the area and attacking military supply lines, provoking the government assault. The Observatory said separate clashes between government troops and deserters in the northwestern town of Kfar Takharim saw two civilians killed and two troop transport vehicles set ablaze.

The activist group said eight people were killed across Syria Sunday, while the opposition Local Coordination Committee put the death toll at 18. It was impossible to independently verify either count.

Meanwhile, several regions across Syria observed the opposition's call for a general strike Sunday, the first working day of the week.

Rights groups said security forces attempted to open shops by force and carried out arrests in several towns, although most business continued as usual in the capital, Damascus, and in the commercial hub of Aleppo. In the southern city of Daraa, army troops and militiamen loyal to Syrian President Bashar al-Assad broke up the strike.

Activists called the nationwide action in an attempt to bring down the regime through civil disobedience. The opposition Local Coordination Committee has urged citizens to gradually escalate the protests by holding sit-ins, closing facilities and refusing to work in the public sector.

Also Sunday, fallout from the anti-government protests spilled over into neighboring Jordan, where a crowd of angry Syrian citizens attacked their country's embassy. The Syrian mission in Amman has been the scene of several protests since the anti-government uprising broke out in Syria nine months ago.

Inside Syria, in the flashpoint city of Homs, an opposition leader said the government has warned protesters to hand in weapons and surrender defecting military members by Monday night or face bombardment. CNN quoted Lt. Colonel Mohamed Hamdo of the Free Syrian Army as saying the 72-hour warning was given on Saturday.

Despite the deadly unrest, Syrians are scheduled to vote for local councils in municipal elections across the country's 14 provinces Monday. The poll is the first test of reforms promised by Mr. Assad's government, which has called for a large voter turnout.

President Assad has been facing mounting international pressure to end a crackdown on dissent that the United Nations says has claimed more than 4,000 lives.