Mr Hariri was killed in a massive blast in Beirut in February 2005
An international court in the Hague has asked Lebanon to hand over documents relating to the murder of the former Lebanese Prime Minister, Rafik Hariri.
The UN-backed tribunal also asked for a list of all suspects Lebanon is holding in connection with the 2005 killings.
The court has been set up to try those suspected of being behind the blast which killed Mr Hariri and 22 others.
The requests bring the tribunal closer to asking Lebanon to hand over four of the suspects within weeks.
The ruling, issued on Monday but only just made public, asked the Lebanese judicial authorities to "defer to the tribunal's competence" in the Hariri case, the AFP news agency reported.
It requested that Beirut "as soon as possible and at the latest within 14 days of receiving this order, refer to the prosecutor the results of the investigation and a copy of the court's records regarding the Hariri case".
Mr Hariri's allies have accused Syria of involvement in his death, a charge Damascus denies.
The court's Canadian prosecutor, Daniel Bellemare, has until the end of April to ask the Lebanese authorities for suspects to be transferred to the Special Tribunal for Lebanon.
Mr Saad has said the tribunal will bring justice for his father
He has said he would submit an indictment when satisfied that he had sufficient evidence.
The four men held in custody were pro-Syrian generals who all held senior positions in the country's security infrastructure.
They are former head of General Security Maj Gen Jamil al-Sayyad, former chief of police Maj Gen Ali Hajj, former military intelligence chief Brig Gen Raymond Azar and Republican Guard commander Mustafa Hamdan.
A trial date has yet to be set and court officials have said proceedings could last for five years.
The tribunal is what many Lebanese have long been waiting for, says BBC correspondent Natalia Antelava in Beirut.
When the court opened in The Hague at the beginning of March, Rafik Hariri's son, Saad, hailed it as a historic day.
"Today the flag of justice for Lebanon is being raised in The Hague," he said.
But some in Lebanon are sceptical about whether the tribunal will ever be able to uncover the full truth, says our correspondent.