BEIRUT (AP) ― The U.N.’s observer mission in Syria was caught up in a burst of violence Tuesday captured on video, with a roadside bomb damaging its cars just minutes after witnesses said regime forces gunned down mourners at a funeral procession nearby.

The mission confirmed its vehicles were hit by a bomb shortly after they met with Syrian rebels, and said there were no injuries.

It was not clear how close the observers were to the funeral shootings, but if confirmed, a regime attack on a civilians directly in front of the observer mission could put pressure on them to describe publicly what they are seeing in Syria. They report back to the U.N. but have not publicized their findings.

The attack in the northern town of Khan Sheikhoun is at least the second time that U.N. observers have been caught up in Syria’s violence. Last week, a roadside bomb struck a Syrian military truck in the south of the country just seconds after the head of the U.N. observers team drove by in a convoy.

A video of the bomb attack was posted by activists online. “The front of a U.N. car took a direct hit,’’ activist Fadi al-Yassin, who witnessed the incident, told The Associated Press. “Everyone ran in panic but the observers stayed in the car. People tried to talk to them but they wouldn’t even open their windows.”

Just minutes earlier, Syrian forces fired on a funeral procession, activists said. Al-Yassin and the Britain-based Syrian Observatory for Human Rights said that as many as 20 people may have been killed and said many others were wounded, some of them in serious condition. It was impossible to independently confirm the toll.

“This is a real massacre and it took place in the presence of U.N. observers,” Rami Abdul-Rahman, head of the Observatory, said of the attack on the funeral. He called for an international investigation and for the monitors to state publicly what they saw.

A video posted by activists online appeared to show the exact moment the U.N. vehicle was struck. The video shows two white vehicles clearly marked “U.N” with people milling around it, and two others parked a few meters behind. Slippers apparently left behind by the mourners running away from the shooting earlier are seen strewn about on the ground.

The blast blew off the front of the first vehicle and sent up a plume of smoke as people screamed and frantically ran for cover. The four cars are then seen slowly driving away.

Ahmad Fawzi, a spokesman for Syria’s special envoy Kofi Annan, confirmed the observers were caught up in the country’s violence as they met with the rebel Free Syrian Army.

“The U.N. Mission in Syria reports that shortly after 2 p.m. local time today, a (U.N.) convoy of four vehicles was struck by an explosion from an improvised explosive device,” Fawzi said in a statement. “Three U.N. vehicles were damaged. No U.N. personnel were injured.”

The Syrian uprising began in March 2011 with mostly peaceful protests calling for change, but a relentless government crackdown led many in the opposition to take up arms. Some soldiers also have switched sides and joined forces with the rebels.

World powers have backed a peace plan that was put forward by Annan, but the bloodshed has not stopped. More than 200 U.N. observers have been deployed in Syria to oversee the truce between the government and armed rebels.

The U.N. estimates the conflict has killed more than 9,000 people.

U.N. spokesman Hassan Seklawi said 211 military observers as well as 66 civilian U.N. staffers working for the observation mission have been deployed in the country, with teams based in major cities such as Aleppo, Hama, Idlib, Deir el-Zour, Daraa and Homs.

The number of military observers is expected to reach the maximum of 300 later this month.

Burhan Ghalioun, the head of Syria’s opposition umbrella group, the Syrian National Council, called for decisive action to enforce Annan’s peace plan, warning it risked failure. He spoke Tuesday in Rome, where the SNC re-elected him to another three-month term during a conference of council members.

An international aid agency meanwhile warned Tuesday that Syrian forces are targeting medical workers and patients who were wounded in the 14-month-old conflict, forcing doctors to scramble to help the injured in makeshift clinics.

Medecins Sans Frontieres, or Doctors Without Borders, which is not authorized to work in Syria, sent teams into the country secretly. They reached the rebellious areas of Homs and Idlib, where they found patients and doctors at risk of attack and arrest.

“Being caught with patients is like being caught with a weapon,” the group quoted an orthopedic surgeon as saying in an Idlib village. There have been previous reports of authorities targeting medical facilities, health workers and their patients in Syria.

The Observatory and the Local Coordination Committees activist group said Tuesday at least three people were killed in an explosion the night before in the Syrian coastal city of Banias, home to one of the country’s two oil refineries. The explosion destroyed a building but the nature of the blast was still not clear, the Observatory said.

The state-run news agency, SANA, said the blast happened when terrorists were preparing a bomb killing the three who working arranging it, as well as a 3-year-old boy.

The Observatory and the LCC also reported shooting by government troops in the eastern city of Deir el-Zour near the border with Iraq that left at least three people dead. They added that the rebel-held central town of Rastan was again under intense shelling by government troops.

U.N. military observers on their way to the central city of Hama on Monday reported heavy fighting in Rastan and nearby Talbiseh, and convinced government forces to re-open a highway they had been blocking, according to a statement from the U.N. in New York.

Across the border in Lebanon, Lebanese troops deployed Tuesday in tense areas of the northern city of Tripoli after three days of sectarian clashes killed at least eight people in a spillover of the conflict in Syria. Officials said two of the eight people died of their wounds overnight.

Lebanon and Syria share a complex web of political and sectarian ties and rivalries, which are easily enflamed as Sunni Muslims who support the rebels trying to oust Assad battle members of the tiny Alawite sect, followers of an offshoot of Shiite Islam who are Assad’s most loyal supporters.

Meanwhile, the U.N’s humanitarian affairs chief said that more than 1 million Syrians need assistance, but negotiating the delivery of aid has been “very slow’’ because the regime wants the Syrian Arab Red Crescent to control it.