A U.N. investigation has implicated senior Syrian and Lebanese officials in the assassination of Lebanon's leading reformer in a move that U.S. and European officials expect will generate new international pressure on the Syrian government of President Bashar Assad.

In blunt language, the report by German prosecutor Detlev Mehlis concluded that the Valentine's Day bombing of former prime minister Rafiq Hariri and 22 others "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 forces."

The report faulted Damascus for failing to fully cooperate with the probe and cited several officials, including Foreign Minister Farouk Charaa for attempting to mislead the investigation by providing false or inaccurate statements. Nevertheless, Mehlis said many leads now point directly to Syrian security officials.

The findings have been eagerly awaited by U.S. and European officials. Along with a second U.N. report on Lebanon due in days, key members of the Security Council hope to use the findings to increase pressure on the Assad government to end years of meddling in Lebanon and to generally change its behavior both at home and throughout the region, including ending support for extremist groups.

Mehlis concluded that the complex assassination plot involved several months of preparation and was conducted by a sophisticated group with "considerable resources and capabilities." Although the primary motive was political, some of the perpetrators may have been motivated by issues involving fraud, corruption and money laundering, he added.

Syrian officials have repeatedly denied any role in Hariri's slaying. Earlier this week, Syrian Ambassador Imad Moustapha said, "We are absolutely categoric in saying we had nothing to do with Hariri." Messages to Syrian officials in Washington and at the United Nations were not returned last night.

But Mehlis said the slaying followed a "growing conflict" between Hariri and senior Syrian officials, including Assad. Tensions came to a head during a 10-to-15-minute meeting between the two men on Aug. 26, 2004. The Syrian leader informed Hariri that he wanted to extend for three years the term of Lebanese President Emile Lahoud, a close ally of Damascus, in defiance of the Lebanese constitution -- a move Hariri firmly opposed.

Mehlis's report included excerpts of interviews and statements about the meeting, including several by Hariri's associates and his son, alleging that the Syrian president threatened Hariri if he opposed the plan. Saad Hariri said his father told him that Assad said: "This extension is to happen, or else I will break Lebanon over your head."

In a conversation between Hariri and a Syrian deputy foreign minister tape-recorded on Feb. 1, the former prime minister recalled the meeting with Assad as "the worst day of my life." Hariri then told the Syrian official that Lebanon would no longer be ruled from Syria.

Walid Mouallem, the Syrian official and a former ambassador to Washington, warned Hariri that Syrian security services had him cornered and not to "take things lightly," according testimony given to the commission. Two weeks later, Hariri was dead.

When the commission tried to follow up these leads, Syria refused to provide substantive information, Mehlis reported. Assad refused to be interviewed. And interviews conducted last month produced "uniform answers" that contradicted the weight of evidence, he added.

The commission cited one witness's testimony that a white Mitsubishi with a tarpaulin over its flatbed was used as the bomb carrier and crossed into Lebanon from Syria three weeks before the attack. It was driven by a Syrian army colonel, the report said. The day before the bombing, the same witness said he drove a Syrian officer to the St. George area of Beirut on a "reconnaissance exercise" -- in the area where the assassination took place.

The report listed several officials who witnesses alleged knew about or played an advance role in the assassination. They included Gen. Jamil Sayyed, Gen. Mustapha Hamdan, Gen. Raymond Azar -- senior Lebanese officials who have been arrested -- and Gen. Rustum Ghazali, Syria's most recent intelligence chief in Lebanon. The day before the assassination, the report said, witnesses allege that Ghazali met with the head of Hariri's protection detail, emerging "badly shaken."

Another witness said Hamdan had accused Hariri of being pro-Israeli and had said, "We are going to send him on a trip, bye, bye Hariri." After Hariri's assassination, the witness was "strongly reminded not to discuss the conversation with anyone," the report said.

The report also cited an allegation by one witness against Assad's brother-in-law, Maj. Gen. Asef Shawkat. The unidentified witness told the commission that Shawkat forced an Islamic militant, Abu Adass, to record a tape claiming responsibility for the bombing two weeks before it occurred, to create the misimpression that the attack was the act of a lone suicide bomber.

Peppered with riveting detail, the report said Syrian and Lebanese intelligence officials wiretapped Hariri's phone.

But the 54-page report said the full picture would require a more extensive investigation, and called for the international community to help Lebanese authorities continue the probe. U.N. Secretary General Kofi Annan announced late yesterday that he will extend the Mehlis mandate to Dec. 15.

The Bush administration said it would not immediately comment. "We intend to read and study it tonight very carefully and decide tomorrow in consultations with other interested governments what the next steps will be," said U.S. Ambassador John R. Bolton. Diplomats expect the report to lead the Security Council to consider action, however.

A second U.N. report on Lebanon is expected next week. It will focus on the implementation of Resolution 1559, which calls for the end of Syria's meddling in Lebanon and the disbanding of armed groups that are tied to Syria.

To follow up on both reports, the United States and other nations have been discussing language for two resolutions that could be introduced as soon as next week to hold the perpetrators to account and add new pressure on Syria, according to U.S. and U.N. officials.

Mehlis's probe included more than 400 interviews and reviews of more than 16,000 pages of documents. Among those interviewed was Ghazi Kanaan, the former Syrian intelligence chief in Lebanon, who committed suicide last week.

Mehlis warned that many Lebanese fear the international community may not follow through, leaving them vulnerable to the return of Syrian military and intelligence services and a revenge campaign. Recent bombings and assassinations have been carried out "with impunity," deterring potential witnesses from testifying, he said.