A four-vehicle U.N. convoy was struck by a blast from an explosive device Tuesday in Syria, the United Nations said.

No U.N. personnel were injured, but three vehicles were damaged, said Ahmad Fawzi, spokesman for Kofi Annan, special envoy to Syria for both the United Nations and the Arab League.

The attack on the vehicles happened around the same time government forces opened fire on a nearby funeral procession, according to opposition groups.

Twenty-three people were killed and 100 were injured in that attack, Avaaz, one of the groups, said.

Another opposition group, the Local Coordination Committees of Syria, described dozens of people falling to the ground after government forces fired on them using heavy machine guns.

Videos posted on YouTube purported to show what happened. CNN cannot confirm their authenticity.

In one, the U.N. observers' vehicles appear to in the midst of chaos in Khan Cheikhoun, part of Idlib province.

Shoes are strewn about on the street and people can be seen gathering near the stopped vehicles.

Suddenly, there is a loud bang and plumes of smoke drift up into the sky. The camera flashes to what looks to be the front of the U.N. convoy, showing one of the vehicles with its hood now popped open. After a few seconds, the vehicles drive away.

"The Assad army is shelling the observers' vehicles in Khan Cheikhoun!" someone yells.

A second video allegedly shows the attack on the funeral procession. A voice taunts what appears to be security forces.

"Are you going to shoot us, or what? You dogs, shoot!" the man shouts.

Seconds later, the forces open fire and people scatter, fleeing the area.

Idlib was the site of some of the heaviest violence Tuesday, according to the opposition Local Coordination Committees of Syria.

At least 63 people were killed, including 33 in Idlib, eight in Homs, seven in Deir Ezzor, five in Hama, four in Banyas, four in Damascus suburbs, one in Hasakeh and one in Daraa, the group said.

SANA, the state-run news agency, said terrorists were preparing a bomb in Banyas when it exploded, leaving "scores" of people dead or wounded. A 3-year-old child died in the collapse of the building, SANA said.

Two law enforcement personnel were killed -- one in Daraa and one in Homs, the agency reported.

Throughout the uprising against the regime of President Bashar al-Assad, Syria has blamed the violence on "armed terrorist groups."

The jihadist Al Nusra Front has denied a claim that it was behind dual suicide bombings that killed 55 and wounded hundreds in the Syrian capital last week.

A video purportedly from Al Nusra Front released Saturday said that government buildings in Damascus were targeted "because the regime continues to shell residential civilians."

But a statement this week from Al Nusra Front said the video "is full of fabrications."

"We never received any confirmation, acknowledgment or denial from our military sector in the front," the group said.

Dissidents accuse the Syrian regime of staging attacks to smear the opposition and to try to link rebels to terrorist groups such as al Qaeda.

Syrian forces carried out a siege Tuesday at Raqa University in northern Syria after a massive demonstration and fired live ammunition at a college student demonstration in Aleppo, the Local Coordination Committees said.

Some rebels say they have had to sell their cows, cars or their wives' jewelry to buy guns and bullets to fight.