The leading daily an-Nahar said the tribunal ruled that the April 1983 bombing, which killed 63 people, was a political crime covered by a general amnesty for offences committed during the country's 15-year civil war.
Judicial authorities were not available for comment.
Parliament ratified the amnesty, part of a national reconciliation drive to end the 1975-90 civil war, in 1991.
Officials feared the country would fall apart if the alleged war criminals from different factions were put on trial.
An explosives-laden truck driven through the outer gate of the embassy, on west Beirut's Mediterranean seafront, wrecked the building. Sixteen Americans were among the dead.
An-Nahar gave the names of six people whom it said were accused of the bombing. They were never tried.
The court also ruled that the amnesty covers the killing of a French military attache in front of his embassy in the Lebanese capital in 1986.Reuse content