A ring of nine Lebanese and Palestinian suspects has been detained in the case, the sources said.
The sources elaborated on a communique from the Lebanese army's commander in chief saying a terrorist network planning an attack on a "major" embassy had been broken.
A spokeswoman for the U.S. Embassy in Beirut refused to comment on the statement, according to The Associated Press.
The ring is suspected of plotting other attacks in northern Lebanon and the Bekaa Valley, sources said. It also is suspected of planning to kidnap members of Lebanon's parliament and Lebanese government ministers and using them to negotiate the release of 20 people who were jailed three years ago after a gun battle.
The breakup of the group was the result of close coordination between Syrian and Lebanese military intelligence services, sources said. Authorities said it represents a blow against terror.
News of the plot came three days after 25 people -- including eight Americans -- were killed in suicide bombings in Saudi Arabia. Nine suspected suicide bombers also died in Monday's attacks in Riyadh. Saudi and U.S. officials have said al Qaeda is suspected in the attacks.
