The findings drew the first official link between Damascus and the killing of the popular opposition leader.
The exhaustive report into the 14 February car bomb that killed Hariri and 20 others, issued to the UN Security Council late yesterday, will almost certainly inflame tensions in the region.
The council, which is likely to use the report to pressurise Syria to ease its continued influence on Lebanon, is scheduled to discuss the report on Tuesday and may consider sanctions against Syria. Late next week, it will also receive a report from Terje Roed-Larsen, the UN special envoy on Lebanon-Syria, about disarming Lebanese militias.
While the report from chief investigator Detlev Mehlis stopped short of fingering Syrian President Bashar Assad or his inner circle, it accused Syria of failing to co-operate and said the plot to kill Hariri must have had the blessing of Syrian security officials.
The decision to assassinate Hariri "could not have been taken without the approval of top-ranked Syrian security officials and could not have been further organized without the collusion of their counterparts in the Lebanese security services," the report said.
The report includes a single reference to Assef Shawkat, Assad's brother-in-law and the Syrian intelligence chief. According to one witness, Shawkat forced a man to tape a claim of responsibility for Hariri's killing 15 days before it occurred.
That tape was aired on the al-Jazeera satellite channel the day of the blast but was discredited by Mehlis' investigators as an apparent attempt to divert attention from the real perpetrators. The man who made the tape, a Palestinian named Abu Adass, left his home on 16 January and was thought to have been taken to Syria, where he disappeared.
Mehlis was careful not to assign blame but cites witness testimony that strongly implicates several officials as conspiring to assassinate Hariri. Lebanon has already arrested four of them, all Lebanese generals close to Syria.
The report also raised questions about Lebanon's pro-Syrian president, Emile Lahoud, who received a phone call minutes before the blast from the brother of a prominent member of a pro-Syrian group, who also called one of the four arrested generals, Raymond Azar.
Those leads and many others still must be followed up before all the details of Hariri's killing will be known, Mehlis said. He asked for more time to work with Lebanese investigators, and in a letter accompanying the report, UN Secretary-General Kofi Annan said he would extend Mehlis' investigation until 15 December.
In one of the most critical parts of the report, Mehlis said that Syria must cooperate if the continued investigation is to succeed. He accused Foreign Minister Farouk al-Sharaa of having lied in a letter sent to Mehlis' commission, though he doesn't give details.
"If the investigation is to be completed, it is essential that the government of Syria fully cooperate with the investigating authorities, including by allowing interviews to be held outside Syria and for interviewees not to be accompanied by Syrian officials," Mehlis said.
There wasn't a single reference in the report to Syria's Interior Minister Ghazi Kenaan, who had been questioned by Mehlis' team. Syria said he committed suicide last week, but many Lebanese have called the circumstances suspicious.
The US Ambassador John Bolton said shortly after the report's release that the United States has "considered various contingencies" but would decide what to do next only after it had read the report and consulted with "other interested governments."
US State Department spokesman Sean McCormack said: "An initial reading of the report indicates some deeply troubling findings and clearly the report requires further discussion by the international community."
Earlier this week, a US official and two UN diplomats said the United States and France were preparing new Security Council resolutions critical of Syria over its alleged involvement in the assassination and alleged arms funneling to Lebanese militias.
Hariri's death led to demonstrations against Syria and magnified the international pressure on Damascus to withdraw its troops, which it eventually did.
In meticulous detail, the report documents how Hariri's movements and phone conversations had been monitored for months. It casts suspicion on a decision by one of the four arrested Lebanese generals, Ali Hajj, to reduce Hariri's state security detail from 40 to eight in November, 2004.
Mehlis draws attention to Sheik Ahmed Abdel-Al, a prominent figure in the pro-Syrian Al-Ahbash Sunni Muslim Orthodox group, whom he called a "a key figure in an ongoing investigation." Abdel-Al had extensive contacts with top Lebanese security officials before and after the blast, and tried to hide information from investigators.
It was his brother who called Lahoud just before the blast.
The 53-page report goes on to outline Hariri's worsening relationship with Syrian officials and said the motive for his death appeared to have been political. Hariri had fallen out with Syria and eventually resigned in October, 2004, a month after a decision to change Lebanon's laws and extend Lahoud's term.
Pro-Syrian opponents had accused Hariri of being the driving force behind a UN resolution last September which unsuccessful attempted to stop Lebanon's parliament from extending the term of Lahoud, his longtime rival. The resolution also demanded the withdrawal of Syrian troops and intelligence operatives from Lebanon.
The report cites a witness as saying that Lebanese and Syrian officials had decided to assassinate Hariri about two weeks after the UN Security Council adopted the resolution.
One witness said that Brig. Gen. Mustafa Hamdan, another of the four generals under arrest, ended an October, 2004 conversation by saying: "We are going to send him on a trip, bye, bye Hariri."