BEIRUT, Lebanon - The leader of a United Nations investigation into the assassination of Lebanese former Prime Minister Rafik al-Hariri arrived in Beirut on Thursday and was expected to begin his inquiries with a visit to the crime scene. Veteran German prosecutor Detlev Mehlis is also due to sign an agreement with the justice ministry and meet senior officials to prepare for the probe, judicial sources said.

"I'm here on a very difficult mission," he told reporters on arrival. "My team and I will work to find the truth."

Mehlis arrived with four members of an overall team of around 50, which will include up to 40 investigators.

The U.N. Security Council authorized an investigation into Hariri's Feb. 14 assassination after a U.N. fact-finding mission decided Lebanon's own inquiry was "seriously flawed."

A U.N. resolution gives Mehlis three months to complete the investigation, although the Security Council can grant him an extra three months if he needs more time.

Many Lebanese blamed Syria for Hariri's assassination in a truck bomb blast that killed at least 20 people in Beirut.

Syria denied any involvement in the attack, which united Lebanon's disparate anti-Syrian opposition behind calls for Damascus to pull its troops and intelligence agents out of Lebanon after 29 years. The last Syrian troops left a month ago.

An international inquiry into Hariri's killing was one of the opposition's main demands. Other assassinations during and after the 1975-1990 civil war have gone largely unpunished.

Mehlis was chief prosecutor at the attorney general's office in Berlin when U.N. Secretary-General Kofi Annan chose him to lead the investigation.

He has 25 years of experience as a prosecutor in cases involving terrorism and organized crime.  (Agencies)