Lebanese authorities have informed the special court investigating the assassination of former Lebanese prime minister Rafik Hariri they are unable to arrest four suspects, all members of Hezbollah, or serve them with indictments.

On Thursday, court President Antonio Cassese appealed to the four men to hire lawyers and turn themselves in — or at least make themselves available by video link to participate in their trial.

"The march to justice is inexorable, and one way or another we will end up with a trial," Cassese said in a public appeal issued by the court located in the Netherlands Thursday.

'Any claim that the tribunal is under the influence of some countries is simply preposterous. We are only acting in the interest of Lebanon.' —Antonio Cassese, UN-backed tribunal head

In June, the Special Tribunal for Lebanon indicted the four members of the Iranian-backed Shiite militia for alleged involvement in the Feb. 14, 2005, truck bombing that killed Hariri and 22 others — a number that includes the suicide bomber.

Hezbollah has denied involvement and said it will never turn over the suspects. Hezbollah leader Sheikh Hassan Nasrallah has called the tribunal's investigation a conspiracy by Israel and the United States.

"Any claim that the tribunal is under the influence of some countries is simply preposterous. We are only acting in the interest of Lebanon," Cassese wrote.

The four suspects include Mustafa Badreddine, a Hezbollah commander who is the suspected bomb maker who blew up the U.S. Marine barracks in Beirut in 1983, killing 241 Americans.

The other suspects are: Salim Ayyash, also known as Abu Salim; Assad Sabra and Hassan Anise, who changed his name to Hassan Issa.

The suspects have until September to make an arrangement with the tribunal, otherwise the case will proceed in their absence with court-appointed defence lawyers. The tribunal, based in Leidschendam outside The Hague, can hold trials in absentia if suspects cannot be arrested.

"It is extremely important for you to appoint legal counsel and to instruct them," Cassese said in the open letter. "If you believe this tribunal is illegal or illegitimate, argue this point through legal counsel chosen by you."

The court president offered to make funds available for the suspects to hire top lawyers and legal experts.

"Nothing will deflect or prevent the tribunal from fulfilling its mission," he said, pledging to deliver a fair trial.

The failure by the authorities to execute arrest warrants came as no surprise. Hezbollah is the most powerful political and military force in Lebanon. Its refusal to co-operate with the tribunal led to the downfall of the previous Beirut government led by Hariri's son, Saad Hariri. The new prime minister, Najib Mikati, was Hezbollah's choice for the position.

The murder of Rafik Hariri was one of the most dramatic political assassinations in the Middle East. A billionaire businessman, Hariri was acclaimed for rebuilding Lebanon after its devastating 15-year civil war ended in 1990.