The trial opened in a suburb of The Hague nine years after the huge Beirut blast that killed the billionaire.
"We will proceed as if the accused are present in the courtroom and have pleaded not guilty," judge David Re told the Special Tribunal for Lebanon.
Hariri's son Saad was sat in the courtroom, at the back behind the victims' representative.
Following
The February 14, 2005 seafront blast killed 22 people including Hariri and wounded 226, leading to the establishment by the UN Security Council of the STL in 2007.
Although the attack was initially blamed on Syrian government, but then it was rejected.
However the baseless initial charges, made the Syrian troops left the Lebanese border areas. The scheme was reviewed by many analysts as a plot to weaken the resistance circle in the region against the Zionist regime.
Then, under the pressures of Lebanese pro-Western figures, another court in 2011 issued arrest warrants without any reasonable documents against Mustafa Badreddine, 52, Salim Ayyash, 50, Hussein Oneissi, 39, and Assad Sabra, 37, all members of Hezbollah resistance group.
A video was then delivered to the Beirut office of pan-Arab satellite broadcaster Al-Jazeera in which a man falsely claimed to be a suicide bomber on behalf of a fictional fundamentalist group called 'Victory and Jihad in Greater Syria'.
Despite Hezbollah resistance group’s clear and continuous declarations, in which it was warned that the Western-backed plots are to target the unity of Lebanese groups, some groups are seeking to put the blame behind Hezbollah.
They will aim to prove the four men's involvement through tracking their alleged use of mobile phones before, during and after the attack.
The Hezbollah resistance has denied 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.
NJF/NJF