AMMAN — 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 a resident said.

The fall of Raqqa, capital of the province by the same name 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 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 spilled 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.

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 ambush inside Iraq illustrates how Syria's conflict, with its sectarian overtones, has the potential to spill over its borders and drag in neighboring countries, further destabilising an already volatile region.

Iraq's Anbar province is experiencing renewed demonstrations by Sunnis against the government of Shiite Prime Minister Nuri al-Maliki over what they see as the marginalization of their minority and misuse of terrorism laws against them.

Syria's rebels are mostly Sunnis fighting to topple President Bashar al-Assad's government, dominated by Alawites, an offshoot of Shiite Islam.

Some 70,000 people have been killed in Syria and nearly a million have fled the country, the United Nations says.

By pushing into Raqqa, the rebels could bring new hazards to hundreds of thousands of Syrians who have fled their homes to the city, now called the "hotel'' of the country.

Residents of the northeastern city, home to half a million people, had pleaded with rebels not to enter the densely built metropolitan area, fearing that Assad's war planes and artillery could target residential areas.

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.

Opposition activist photographs showed a burning guard post, men ripping down a poster of Assad and a fallen statue of his late father, Hafez al-Assad, who took power in 1970.

Video footage posted on the Internet by rebel groups showed an abandoned prison in what they said was the center 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."

In a statement, the council said that with the fall of Raqqa a link was established between vast areas that fell to the opposition in the oil-producing east of the country and rebel-held regions in the northern Aleppo and Idlib provinces.

Events in Raqqa were not confirmed by independent media, which are restricted in their access to combat zones.

International powers are divided over Syria, with Russia and Shiite Iran supporting their historical ally Assad and the United States and Sunni Gulf countries backing the opposition.

Saudi Arabia and Qatar are widely believed to be providing weapons to the rebels, but the United States says it does not wish to send arms for fear they may find their way to Islamist hardliners who might then use them against Western targets.

U.S. Secretary of State John Kerry, who said last week that Washington would directly provide medical supplies and food to rebels, reiterated that concern on Monday.

"There is no guarantee that one weapon or another might not at some point in time fall into the wrong hands,"he told a joint news conference with Saudi Foreign Minister Prince Saud al-Faisal in Riyadh.

"Believe me the bad actors regrettably have no shortage of their ability to get weapons, from Iran, from Hezbollah, from Russia unfortunately, and that is happening," Kerry said.

Faisal, without confirming the supply of arms to rebels, said Saudi Arabia would do "everything within its capabilities'' to provide "aid and security for the Syrians."

Also contributing to this Reuters report were Oliver Holmes in Beirut, Kamal Naama in Anbar and Angus McDowall in Riyadh; Editing by Robin Pomeroy and Stephen Powell.