DAMASCUS - The incessant violence in Syria extended its reach on Tuesday and targeted the UN observers who were supposed to have a "calming effect" in restive Syrian areas.

Shortly after 2 pm local time (GMT 1100) on Tuesday, a UN convoy of four vehicles was struck by a blast caused by an improvised explosive device in Khan Sheikhoun area, located near Syria's central province of Hama, Ahmad Fawzi, spokesman of the UN-Arab League joint envoy Kofi Annan, said in a statement obtained by Xinhua.

Three UN vehicles were damaged, but no UN personnel were injured, Fawzi said, adding that the mission has sent a patrol team to the area to extract those observers.

Earlier, Syria's mainstream media said an explosive device ripped through a UN convoy, injuring two observers and damaging two vehicles. The Syrian army has intervened, clashed with armed groups there and managed to move the observers to a safe zone.

The head of UN observers mission to Syria said Tuesday that the number of military observers has exceeded 200, stressing that the observers are tracking and documenting all violations to the cease-fire brokered by Annan, according to state-run SANA news agency.

While efforts are being exerted to find a political and peaceful solution to Syria's 14-month-old unrest, clashes and killings were still reported as of Tuesday.

A three-floor building in the coastal city of Banias collapsed Tuesday when an explosive device under preparation by "terrorists" inside the building exploded, according to SANA.

As SANA said the blast caused unspecified number of casualties, the opposition Britain-based Syrian Observatory for Human Rights said at least three people were killed in the Banias explosion.

In southern Daraa province, two law-enforcement personnel, including an officer, were killed after an "armed terrorist group" detonated two explosive charges and opened fire at their patrol, while in central Homs province, an armed terrorist group assassinated a brigadier general near Shinshar crossing on the Homs-Damascus highway.

In the meantime, the Syrian authorities foiled an infiltration attempt from the Turkish territories by armed groups at al-Duria post near the northwestern province of Idlib. Border guards clashed with the gunmen, killing and wounding scores of them.

The prolonged violence in Syria has undermined the work of UN observers who began to arrive in Syria in April to monitor the cease-fire deal brokered by former UN chief Annan.

The cease-fire, which went into effect on April 12, has been shaky from the very beginning as mutual mistrust between the government and the opposition has overwhelmed the endeavors to solve the crisis politically.