The explosion took place in the city of Baalbek, the birthplace of Hezbollah, some 15 kilometers (9 miles) from the Syrian border.

A statement from the local Hezbollah office said Hafez Hassan, a bus driver for the Abbas Mussawi School, found "a strange object from the remnants of the Israeli aggression" outside the school's walls and brought it into the building, where it exploded.

The school official, speaking on condition of anonymity because he was not authorized to speak to the media, said the explosion was confined to one room.

Hassan died instantly and the school's deputy principal, Fahed Yaghi, was rushed to a hospital where he is in critical condition, the Hezbollah statement said.

Lebanese police and army troops cordoned off the school compound, preventing staff and students from leaving the premises while an investigation was under way, it added.

Israel has been accused of firing as many as 4 million cluster bombs into Lebanon during last summer's Israel-Hezbollah war. United Nations demining experts say up to 1 million cluster bombs failed to explode immediately and continue to threaten civilians.

A stronghold of the militant group Hezbollah, Baalbek was repeatedly hit by Israeli airstrikes during last summer's war, which ended with a U.N. brokered cease-fire on Aug. 14.

Picture: A German bomb dispossal expert inspects a cluster bomblet that was found in the Lebanese village of Sultaniyeh

Source: AP