Arrests have been made in Lebanon in connection with the twin bus bombings last month which killed three people.
The blasts occurred in a Christian area in the mountains east of Beirut
Security officials said four members of a little-known radical Palestinian group, Fateh al-Islam, had confessed, while one suspect remained at large.
They said the four men who were arrested were Syrians.
The attacks took place a day before the commemoration of the assassination of former Prime Minister Rafik Hariri, who was killed in a massive blast in 2005.
Lebanese Interior Minister Hassan al-Sabaa said the group was known to have close ties with the Syrian intelligence agency, but he said it was unclear who ordered the attack.
In February, a bomb was placed on each commuter bus and exploded as the vehicles drove through a Christian area in the mountains east of the capital, Beirut.
Mr Sabaa said the group had also planned to carry out an attack against the offices of the nearby Christian Phalange Party, which is allied to the government and opposed to Syria.
A leader of the Phalange Party, Minister Pierre Gemayel, was shot dead in Beirut last year. His killing was widely blamed on Damascus.
Syria has denied involvement in the 16 attacks Lebanon has witnessed in the last two-and-a-half years.
A spokesman for Fatah al-Islam also denied any link to the bus bombings, saying the group was being used as a scapegoat.
The BBC's Kim Ghattas in Beirut says Syria's allies in Lebanon in the opposition have often accused the anti-Syrian government of trying to frame Damascus.