The interim report by UN chief investigator Serge Brammertz also expanded on links previously found between the Hariri slaying and some 14 other attacks against anti-Syrian Lebanese figures between October 2004 and December 2005.
The report, which Mr Brammertz personally delivered to UN chief Kofi Annan, estimated that a suicide bomber detonated up to 1,800 kilograms of explosives, placed in a Mitsubishi van, during the February 2005 attack that killed the billionaire former premier and 22 others on the Beirut seafront.
"The Commission continues to finalise its primary crime scene work, including its forensic research and analysis, and is satisfied that it has largely established the facts to an evidential standard," the report said.
The report also noted further Syrian cooperation with the probe.
"We think it is important ... a sign of real progress," US Ambassador to the UN John Bolton told reporters, saying this indicated that UN investigators were "getting closer and closer to getting ready for trial".
Mr Bolton also highlighted the probe's findings of more evidence of a link between the Hariri assassination and 14 other attacks carried out in Lebanon against opponents of Syria.
"The commission's work in relation to the 14 other cases helps place the attacks into the prevailing context at the time, and is beginning to produce links notably in identifying potential conjoining motives," the report said.
"Establishing the depth, breadth and nature of those links to an evidential standard is an investigation priority over the next months."
The 14 cases, which Lebanese authorities have been probing with UN help, include assassinations and assassination attempts targeting anti-Syrian Lebanese figures, as well as attacks on commercial interests.
Syrian cooperation
The UN report, which was relayed to the 15 members of the UN Security Council before it was made public, also said investigators remained generally satisfied with the cooperation of Syria.
"The cooperation that the commission has received from the Syrian Arab Republic has remained generally satisfactory and the commission continues to require its full support in providing information and facilitating interviews with individuals located on Syrian territory," it said.
A report by Mr Brammertz's German predecessor, Detlev Mehlis, had implicated senior officials from Syria, which for decades was the power broker in its smaller neighbour. Damascus strongly denies any connection with the Hariri slaying.
Mr Brammertz, a Belgian prosecutor, was expected to brief the Council on Friday about his latest findings.
Last June, the Security Council extended the mandate of the Brammertz-led enquiry panel until June 15, 2007 at the request of the Lebanese government.
Two weeks ago, an exiled former Syrian intelligence officer was quoted as saying Syrian President Bashar al-Assad and his Lebanese counterpart, Emile Lahoud, ordered the Hariri murder.
"Bashar al-Assad and Emile Lahoud gave the orders for Hariri's murder," Mohammed Zuhair as-Saddiq was quoted by the Beirut daily An-Nahar as saying in an interview with the Dubai-based Al-Arabiya satellite television channel.
Saddiq, a former colonel in Damascus' intelligence service who was speaking from the French capital Paris, also claimed that "former Lebanese officials and certain Arab officials", whom he did not identify to Al-Arabiya, "also participated in this crime".