Syrian opposition fighters captured the northeastern city of Raqqa on Monday and crowds toppled a statue of President Bashar al-Assad's father, opposition sources and residents said.
The fall of Raqqa on the Euphrates River would be a significant development in the two-year-old revolt against Assad. The rebels do not claim to hold any other provincial capitals.
Rebel fighters said loyalist forces were still dug in at the provincial airport 60 kilometres from Raqqa and they remained a threat. A resident said that a Syrian military intelligence compound in the town was not in rebel hands but was surrounded by anti-Assad fighters.
On Monday the civil war burst into neighbouring Iraq, where officials reported that gunmen had killed at least 40 Syrian soldiers and government employees as they headed home after fleeing a Syrian rebel advance last week.
Around 65 Syrian soldiers and officials had handed themselves over to Iraqi authorities on Friday after rebels seized the Syrian side of the border crossing at the Syrian frontier town of Yaarabiya.
Iraqi authorities were taking them to another border crossing further south in Iraq's Sunni Muslim stronghold, Anbar province, when gunmen ambushed their convoy, a senior Iraqi official told Reuters. No group has claimed responsibility.
"The incident took place in Akashat when the convoy carrying the Syrian soldiers and employees was on its way to the al-Waleed border crossing," a senior Iraqi official told Reuters.
"Gunmen set up an ambush and killed 40 of them, plus some Iraqi soldiers who were protecting the convoy."
A member of Anbar's provincial council, Hikmat Suleiman Ayade, put the number of people killed at 61, including 14 Iraqis who were protecting the convoy.
At the United Nations on Monday, Israel warned that it could not "stand idle" as the Syrian conflict spilled over borders. Israel's U.N. ambassador complained to the 15-member Security Council about shells from Syria landing in Israel.
Syria's rebels are mostly Sunnis fighting to topple Assad's government, dominated by Alawites, an offshoot of Shi'ite Islam that has controlled Syria since the 1960s.
Some 70,000 people have been killed in Syria and nearly a million have fled the country, the United Nations says.