Judges at the Special Tribunal for Lebanon on Wednesday said in an appeal ruling that the court could try four members of the powerful Hezbollah movement for the murder of former Lebanese prime minister Rafiq Hariri.
Lawyers for the four men argue that the UN-backed court set up to try them has no jurisdiction in the case.
But on Wednesday the appeals chamber of the Special Tribunal unanimously dismissed arguments submitted by the defence that the court was illegal, the tribunal said in a statement.
Defence lawyers launched a bid to have the court declared illegal in June, saying the UN Security Council had abused its powers when it set up the tribunal five years ago.
Signup to our newsletter and follow us on Facebook and Twitter!
In June last year, the court issued warrants for Moustafa Badreddine, 50, Salim Ayyash, 48, Hussein Anaissi, 37, and Assad Sabra, 35, and Interpol has also issued a "red notice" for the suspects.
But Lebanon has not arrested them.
Billionaire politician Hariri was killed in 2005 in a massive car bombing on the Beirut seafront along with 22 other people, including the suicide bomber.
Hezbollah has denied any responsibility for the attack, and its leader Hassan Nasrallah has dismissed the tribunal as a US-Israeli conspiracy, vowing that none of the suspects will be arrested.
Hezbollah, a close ally of Syria, is the most powerful faction in the Lebanese cabinet, and its militia the most powerful military force in Lebanon.