Syrian opposition fighters captured the northeastern city of Raqqa on Monday and crowds toppled a statue of President Bashar 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.
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Rebel fighters said loyalist forces were still dug in at the provincial airport 60 km (40 miles) 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 neighboring 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.
Raqqa residents destroy statue
"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.
The ambush inside Iraq illustrates how Syria's conflict has the potential to spill over its borders and drag in neighbors.
Iraq's Anbar province is experiencing renewed demonstrations by Sunnis against the government of Shiite Prime Minister Nuri Maliki over what they see as the marginalization of their minority and misuse of terrorism laws against them.
Maliki boycotted Assad and pulled the Iraqi ambassador from Damascus before the Syrian revolt erupted in March 2011 for what he described as Syrian support for Sunni extremists and foreign jihadists responsible for deadly attacks on Shiite civilians.
But the Iranian-backed Iraqi premier has not sided with other Arab states backing the Sunni-led uprising in Syria, saying that the upheaval threatened regional stability.
At the United Nations on Monday, Israel warned that it could not "stand idle" as the Syrian conflict spilled over borders. Israel's UN 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 Shiite 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.
In what could be a new danger for the millions of Syrians who have fled their homes but remain inside the country, rebels pushed into Raqqa, a city known as the "hotel" of the country after thousands of displaced families fled there.
Some residents of the northeastern city, home to half a million people, had pleaded with rebels not to enter Raqqa, fearing that Assad's war planes, artillery and missiles could target residential areas.
"The fear now is that the regime will hit Scud missiles indiscriminately at Raqqa to punish the population," said Nawaf al-Ali, the Raqqa representative in the Syrian National Coalition, an umbrella of the main opposition groups.
Video footage taken by opposition activists showed youths climbing on the Hafez al-Assad statue in Raqqa's central square and tying a rope around its head.
"A crowd of hundreds braved the fighting and marched on the main square and took down the statue," said one of the residents, himself a refugee from the city of Deir al-Zor.
One video showed rebels guarding the city's museum, housed in a French colonial era palace, which, along with the city's horseshoe shaped wall, give a glimpse of Raqqa's past.
Raqqa, founded by Alexander the Great, once acted as a Byzantine front line against Persia. It was designated by Al-Mansour, the founder of the Abbasid empire, as the second Arab capital after Baghdad.
It has long been in decline. A water crisis before the revolt resulted in the internal displacement of hundreds of thousands of people from Raqqa and the rest of Syria's east and prompted the United Nations to send food aid to the region.
Assad's father, the late President Hafez Assad, who ruled Syria with an iron fist for 30 years, used a carrot and stick approach to build alliances between the ruling hierarchy and Sunni Muslim tribes in Raqqa and the neighboring province of Deir al-Zor. These alliances have broken down.
The Syrian Observatory for Human Rights, a Britain-based monitoring group, said the Islamist Jabhat al-Nusra and other rebel groups launched the offensive on Saturday and large parts of Raqqa were now under rebel control.
Video footage posted on the Internet by rebel groups showed an abandoned prison in what they said was the centre of the city, 100 miles east of Aleppo.
The Syrian National Council, a large bloc within the umbrella Syrian National Coalition, said the capture of Raqqa would prove "a decisive victory in the struggle for the downfall of the criminal Assad regime and to salvage Syria from the ugliest epoch in its history".
Events in Raqqa were not confirmed by independent media, which are restricted in their access to combat zones.