Five Spanish peacekeepers, three of whom are of Colombian origin, killed in a roadside bomb in southern Lebanon on Sunday, Spanish Defense Minister Jose Antonio Alonso announced.

They were injured by the explosion of two devices when their vehicle detonated a mine south of the country, Alonso said in a press conference.

He said all five killed were in the Spanish army and were part of the UN force in south Lebanon. It was the first deadly attack on the UN force since last year's Israel-Hezbollah war.

"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," Alonso said.

The incident occurred at Sahel al Derdara, a hamlet near aJiam, the largest in the security limits patrolled by the Spanish soldiers deployed in Lebanon integrating the United Nations' Interim Force in Lebanon (UNIFIL).

Spanish media quoting Lebanese military sources reported the Spanish militaries' vehicle detonated a mine placed in the highway between the localities of Marjayun and aJiam, six kilometers north of the Israeli border city of Metulla.

The eyewitnesses said the first explosion was followed by a second explosion some minutes later and it is believed it was either the gasoline tank or the ammunition they were transporting.

It is still ignored if the explosion was caused by an old mine or if it was a deliberate attack against the UNIFIL troops.

This is the only Spanish mission of this type authorized by the government of Jose Luis Rodriguez, it was approved by the Ministers' Council on December 1 of 2006.

The UNIFIL now has 13,000-strong troops in Lebanon , which has been fulfilling a peacekeeping task since last summer's Israel- Hezbollah conflict. The Spanish battalion deployed in Lebanon is integrated by 1,100 troops.

(Xinhua News Agency June 25, 2007)