A UN probe has found evidence pointing to Syrian and Lebanese links in his bomb death - claims which both deny.
The UN Security Council will discuss the report and could impose sanctions.
But the UN investigator who wrote the report has had to defend his decision to remove the names of five top Syrians from one section of the final draft.
The names included those of the brother and brother-in-law of Syrian President Bashar al-Assad - Maher al-Assad and Asef Shawkat.
German Detlev Mehlis insisted at a hastily-arranged news conference that the names had been removed only to maintain their "presumption of innocence", once he learned that his confidential report was to be made public.
In the removed section, a witness names the presidents' relatives as being among five senior Syrians who decided in 2004 to kill Mr Hariri.
The names of three of the five men - plus other senior Syrian and Lebanese officials - remain elsewhere in the report, some accused by witnesses of direct involvement in the plot to kill Mr Hariri.
The report also concluded that the Syrian government had not co-operated fully with the inquiry.
In the US, President Bush said the UN should convene a session as soon as possible to discuss the report.
"Today, a serious report came out that requires the world to look at it very carefully and respond accordingly," he said.
Earlier, US Secretary of State Condoleezza Rice said the international community would have to "seriously consider how it demands accountability".
'False information'
The report, prepared at the request of UN Secretary General Kofi Annan, says the car bombing that killed Mr Hariri could only have been carried out by a group with extensive organisation.
As well as evidence pointing to Syrian involvement, the UN investigators also said they had also found evidence of Lebanese collusion in Mr Hariri's death in February.
The question for us all now is what sanctions can we bring against the guilty?
Mr Hariri's assassination - for which the likely motive was political - was complex and had obviously been planned for months, the report says.
The UN Security Council will be briefed on 25 October by Mr Mehlis.
Both Syria and Lebanon have denied the allegations of official involvement.
Syria's Information Minister Mehdi Dakhlallah condemned the findings as "politically biased" deceptions and said the report was "far from the truth".
The Lebanese presidency issued a statement denying that the brother of a key figure in the inquiry had called President Emile Lahoud minutes before the truck bomb exploded.
"The press office in the presidential palace categorically denies this information, which has no basis in truth and is a part of a pressure campaign against the president," it said.
'Impending crisis'
Syria was the main power in Lebanon until its military withdrawal earlier this year in the wake of an international outcry over Mr Hariri's death.
The BBC's Ian Pannell in Damascus says it is widely believed that the Syrian authorities were angered by Mr Hariri's growing opposition to their influence in Lebanon.
Although President Assad has consistently denied any involvement in the killing, the report will add to the sense of impending crisis felt in the country, our correspondent says.
Syria finds itself almost completely isolated, with little support from other Arab nations, and faces the prospect of crippling UN sanctions, he adds.
Since Mr Hariri and 22 other people were killed on 14 February, a series of bomb attacks has targeted anti-Syrian journalists and politicians as well as Christian areas in Lebanon.
Mr Hariri's son, Saad, has said he wants those implicated by Mr Mehlis' report to be tried by an international court.
Troops have been deployed in the Lebanese capital, Beirut, and other cities in case of violence following the inquiry's findings.