Former Lebanese Prime Minister Rafik Hariri was killed by a truck filled with explosives, say UN investigators.
Rafik Hariri was killed by a truck full of explosives, finds a UN probe
The head of the team, Detlev Mehlis, told reporters this contradicted widespread speculation that the explosives were buried under the road.
Some Lebanese believed recent road works near the attack site suggested officials may have been involved in a plot to assassinate Hariri.
His death led to protests calling for the withdrawal of Syria from Lebanon.
Syrian troops withdrew last month following a wave of opposition protests blaming Damascus for the assassination.
Correspondents say the investigators' report opens up the field of possible suspects to beyond Lebanon or Syria.
It is still not clear whether the attack was carried out by a suicide bomber, Mr Mehlis said.
"The explosion was beyond any reasonable doubt above ground," he said. "There was no indication of an underground explosion."
Mr Mehlis, whose team arrived in Lebanon at the end of May, said he would question officials in charge at the time of the attack - including Syrians.
"We will of course investigate everyone who was in one way or another responsible for security in Lebanon at the time of the crime," he said.
Mr Hariri was killed in the bomb attack in Beirut on 14 February, along with 19 other people. Syria denies any involvement.
The investigation continues as Lebanon holds staggered parliamentary elections over four Sundays with the last round being held this weekend.