A U.N. investigation concluded that high-ranking Syrian and Lebanese security officials were involved in the assassination of former Lebanese Prime Minister Rafik Hariri (search), according to a report released Thursday.

The strongly worded report by chief investigator Detlev Mehlis (search) said the two nations' intelligence services kept tabs on Hariri before his assassination by wiretapping his phone, and there was evidence a telecommunications antenna was jammed near the scene of the car bomb that killed him and 20 others on Feb. 14.

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 U.N. Security Council (search) was to discuss the report Tuesday. The United States and France earlier prepared resolutions critical of Syria over the assassination and alleged arms funneling to Lebanese militias, a U.S. official and two U.N. diplomats have said.

The report quotes a Syrian witness living in Lebanon who claimed to have worked for Syrian intelligence in Lebanon as naming several officials who conspired to assassinate Hariri. They included Brig. Gen. Rustum Ghazale, the last Syrian intelligence chief in Lebanon who was in charge when Hariri was assassinated, and Brig. Gen. Mustafa Hamdan, who was Lebanese commander of the Presidential Guards Brigade at the time of the assassination.

Mehlis' team had already named Hamdan and three other Lebanese generals, all close to Syria, as suspects in the assassination, and Lebanon has arrested them. The report did not recommend any other arrests, but it called for the investigation to be extended with Lebanese judicial and security authorities in the lead.

Mehlis' 53-page report accused Syrian authorities of trying to mislead his investigation, and directly accused Foreign Minister Farouk al-Sharaa (search) of lying in a letter sent to his commission.

The commission said Syria's cooperation in form — but not substance — "has impeded the investigation and made it difficult to follow leads established by the evidence collected from a variety of sources."

"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," it said.

In a letter accompanying the report, U.N. Secretary-General Kofi Annan (search) said he would extend Mehlis' investigation until Dec. 15, which would allow the team to continue its work and help the Lebanese authorities.

The U.N. Security Council gave the probe a three-month mandate when it began its work on June 16 but said it could be extended for three more months if necessary. In August, Mehlis received an extension beyond the original Sept. 15 deadline.

Several lines of investigation still need to be pursued, Mehlis said. They include jamming devices in Hariri's convoy that were functioning at the time of the bombing. It appears there was interference with a telecommunication antenna at the crime scene at the time Hariri was killed in a massive car bomb, Mehlis wrote.

U.S. Ambassador John Bolton (search) said the United States would have no immediate comment and would decide what to do next only after it had read the report and consulted with "other interested governments."

"We've obvouisly considered various contingencies but no final decision will be made until we now review the report," Bolton said.

Mehlis' findings come before another report to the council from Terje Roed-Larsen, the U.N. special envoy on Lebanon-Syria about disarming Lebanese militias. U.N. spokesman Stephane Dujarric said it will be delayed until late next week to avoid "congestion."

In Lebanon, authorities had increased security ahead of the report's findings. Many there blame Syria for the Feb. 14 assassination of Hariri, a former prime minister whose motorcade was bombed on a Beirut street, killing him and 20 others. Syria has denied involvement and so have the four Lebanese generals.

Mehlis said the most likely scenario for the activation of the explosives was a suicide bomber. A slightly less likely possibility was a remote controlled device, he said.

Hariri's death led to demonstrations against Syria and magnified the international pressure on Damascus to withdraw its troops, which it eventually did. The Security Council approved a probe into Hariri's assassination on April 8.

The report said a Syrian witness living in Lebanon who claimed to have worked for Syrian intelligence in Lebanon told the commission that "senior Lebanese and Syrian officials decided to assassinate Rafik Hariri" about two weeks after the U.N. Security Council adopted a resolution in September 2004 demanding the withdrawal of Syrian forces from Lebanon.

The witness, who was not identified, claimed a senior Lebanese security official went to Syria several times to plan the crime. At the beginning of January 2005, a high-ranking Syrian officer posted in Lebanon told the witness that "Hariri was a big problem to Syria."

"Approximately a month later the officer told the witness that there soon would be an 'earthquake' that would re-write the history of Lebanon," the report said.