BEIRUT -- Syrian government airstrikes have killed at least 14 people in the northern province of Raqqa less than a week after rebels seized the area's provincial capital, activists said Sunday, while the UN's top official for refugee affairs said the number of people fleeing Syria could triple this year if the war continues.

The city of Raqqa, home to a half million people before Syria's uprising, could prove a test case for how rebels administer areas they capture. The rebel groups that led the battle for the city are strongly Islamist, some of them extremists, and videos released over the weekend indicate some fighters have summarily executed prisoners.

Recent government airstrikes, meanwhile, show the limits of rebel control. Even if they hold the ground, they can do little about the government's air force, which often bombards areas recently captured by the rebels, killing fighters and civilians alike.

Two airstrikes in Raqqa province killed at least 14 people on Saturday, the Britain-based Syrian Observatory for Human Rights said.

A video posted online from Raqqa city showed the dead bodies of seven people scattered in a street with destroyed buildings nearby. An off-camera narrator says they were killed in an airstrike.

The Observatory said at least seven others were killed in a separate air attack near the province's eastern border.

Over the last year, Syria's rebels have greatly expanded the territory they hold in northern Syria, mostly in the provinces of Idlib and Aleppo that abut the Turkish border. In February, they extended their control into Raqqa province, seizing a hydroelectric dam on the Euphrates river. After storming a central prison, they seized most of Raqqa city on March 4, solidifying their control over the next two days.

Raqqa is the first of Syria's provincial capital cities to fall completely under rebel control.

Rebel actions since taking the city have raised concerns about how they will administer the area.

A number of videos have surfaced in recent days that show dead government soldiers and security officials lying on the ground, their heads bearing gunshot wounds.

One video showed rebels driving the dead body of a military intelligence official around in the back of a pickup truck to show it off. At one point, they lay out his body in a street next to another body. Both have large holes in their heads.

"No one hurt me more than this man!" a voice off-camera yells.

Rights groups have reported summary executions of regime officials and troops following the capture of other areas, especially of pro-government militiamen known as "shabiha" whom rebels say are guilty of atrocities. Rebels groups in some area have set up courts to try prisoners, though it is unclear whether they live up to international standards of due process.

Another video from Raqqa posted on Saturday shows three bodies in a street in pools of blood.

"These are the dogs of military intelligence and they were executed in Clock Square," a voice says, referring to a city landmark.

Other captured regime officials appear to have been kept alive.

Another video posted Saturday showed the provincial governor, Hassan Jalalil, along with the head of President Bashar Assad's ruling Baath party sitting in front of the black flag of Jabhat al-Nusra, an extremist rebel group the U.S. has designated a terror group.

The two were captured by rebels when they stormed the governor's palace on March 4.

In the videos, the second man, Suleiman al-Suleiman, says that before his capture he was scared that rebels were extremists.

"But my view has changed, and I have seen that Jabat al-Nusra has a religious program that follows Allah and his prophet," he said.

There was no way to establish if he was speaking under duress.

All videos appeared authentic and corresponded with other reporting by The Associated Press.

Syria's crisis began with anti-regime protests in March 2011 and has since spiraled into a civil war pitting government forces against hundreds of rebels groups.

The Syrian government portrays the war as fueled by an international conspiracy carried out by terrorists that seeks to weaken the country.

Also Sunday, the UN chief for refugees says the number of people fleeing Syria could increase by "two or three times" by the end of the year if the country's conflict doesn't end.

UN High Commissioner for Refugees Antonio Guterres told reporters in the Turkish capital that the international community should work toward ending the conflict.

"If the Syrian conflict will go on and on and on, there is an effective risk of an explosion into the Middle East," he said, adding that it was in "the interest of everybody to stop this conflict before it is too late. "

On March 6, the UN said the number of registered Syrian refugees had reached one million. Guterres also renewed a call for nations to support Turkey, Lebanon, Jordan and other countries sheltering refugees.

The UN says more than 70,000 people have been killed in the violence.