Sunday's blast killed three Colombian officers and three Spaniards, and wounded several other peacekeepers in the first attack in the country since last year's month of bloodshed between the Israeli army and radical Lebanon-based group Hezbollah.
The as-Safir daily said "a very sophisticated" explosive device was used in the attack, for which no groups have yet claimed responsibility. However, according to investigation results so far, the attack bears the hallmarks of al Qaida, the paper said.
The Lebanese government blamed the attack on Syria, while Hezbollah, which enjoys broad public support in southern Lebanon, has started its own investigation, the newspaper said.
Russia said the attack was a slap in the face for the entire international community.
There are now about 13,000 UN peacekeepers deployed in the area, including French, Spanish and Indian troops.