VIDEO - Six UN peacekeepers were killed Sunday and four others were wounded in an explosion in southern Lebanon, Lebanese officials said. Earlier, Spanish Defence Minister Jose Antonio Alonso said two Spanish and three Colombian peacekeepers, all serving in the Spanish army, had been killed in the blast. The ministry later confirmed one of the three Spanish soldiers reported wounded had subsequently died. A police source said a suicide car bomber "most likely" killed the UNIFIL troops, adding that a mangled car was found at the scene with human remains inside. The attack took place between the towns of Marjayoun and Khiam, about six kilometers (four miles) north of the Israeli border town of Metulla. Security sources had said earlier the blast was caused by a roadside bomb detonated by remote control. "We are working on the theory of a terrorist attack. In the last few weeks there have been many incidents which have destabilized Lebanon. We were on high alert and we had stepped up security," the Spanish defense minister said in Madrid. The minister said he would fly to Beirut later to collect the bodies. The attack hit two UN vehicles. Witnesses said ammunition in a troop carrier had exploded after the initial blast. Two soldiers on top of the vehicle were blown dozens of metres (yards) into a field. Two of those who died inside were burnt beyond recognition. There was no immediate claim for the attack, which occurred just hours after Lebanese troops killed seven Islamist militants in a raid on a block of flats in the northern city of Tripoli. Hizbullah condemned the blast and said it was an attack designed to destabilize the country, the group's television station said. "The attack hurts the people of the south and of Lebanon," Al-Manar television said.