Sadr, who founded the opposition Amal movement now led by parliament speaker Nabih Berri, would have been 80 this year and is still regarded by the Lebanese Shiite community as their key spiritual guide.

The case has been a long-standing sore issue in Lebanon, where authorities blame Gadhafi and his aides for their disappearance.

Lebanon last week issued an arrest warrant for Libyan leader Moamer Kadhafi over the disappearance of the imam on August 31, 1978 while he was in Tripoli with two companions, who vanished with him.

"We tell the leader of the Libyan regime Moamer Kadhafi: you are personally responsible for the disappearance of Imam Mussa Sadr," Berri said in a speech to the crowds in the southern town of Nabatiyeh.

"Let no-one think that we will forget or make any compromise," said Berri, a leading figure in the Syrian-backed opposition in Lebanon spearheaded by the powerful Hezbollah movement.

Parliament Speaker Nabih Berri urged Gadhafi to reveal facts in the case. Berri spoke Sunday in a speech at a rally in the southern town of Nabatiyeh on the anniversary of the disappearance.

Libya has denied involvement in Sadr's disappearance, saying he left Libya for Italy. But the Italian government has always denied he ever arrived there.

However, in 2004 Italian authorities returned a passport found in Italy belonging to the imam. -Agencies