President Bush called on the United Nations yesterday to meet urgently to consider taking action against Syria after a U.N. investigation implicated top officials in the regime of President Bashar Assad in the assassination of Lebanon's leading reformer.

In a sign of the sudden escalation in tension between Syria and the international community, Britain yesterday called on the world body to consider punitive sanctions on Damascus. The Security Council is expected to meet Tuesday to consider possible actions for two new resolutions, according to U.S. and U.N. officials.

Bush called the detailed U.N. investigative report into the Feb. 14 killing of former Lebanese prime minister Rafiq Hariri "very disturbing" and asked Secretary of State Condoleezza Rice to immediately convene the foreign ministers of the 15 Security Council members to "respond accordingly" to its allegations.

"The report suggests, strongly suggests, the politically motivated assassination of Prime Minister Hariri could not have taken place without Syrian involvement," Bush said, speaking in front of a piece of the Berlin Wall at the Ronald Reagan Presidential Library and Museum in Simi Valley, Calif.

En route to Alabama with British Foreign Minister Jack Straw, Rice told reporters that the international community must "demand accountability" from Damascus. Intense diplomatic discussions are expected to continue through the weekend among U.S., British, French and Russian officials to broker a consensus behind potential punitive action, according to U.S. and U.N. officials.

Ideas under discussion range from a ban on Syrian international flights and trade limitations to an embargo on goods that can be used for military purposes, according to Western officials familiar with the diplomacy who spoke on the condition of anonymity. Envoys are also considering demanding that Assad, who inherited power from his father in 2000, require those named in the report to help in the investigation -- or take action himself against them.

At the United Nations, U.S. Ambassador John R. Bolton said pursuing the investigation is the first priority for the Security Council. "In the absence of serious Syrian cooperation on substantive matters, the mission can't get to the ultimate truth," Bolton said. "That is what it seems to me the focus [of] the U.N. Security Council should be. . . . We need to look at other steps to obtain Syrian cooperation."

The United Nations may lay out a series of steps Syria must take over a limited time, giving it an opportunity to more fully cooperate with investigators, Western envoys said. Secretary General Kofi Annan has extended the investigation, conducted by German prosecutor Detlev Mehlis, through Dec. 15. But a senior U.S. official involved in the diplomacy said discussions are still "in their infancy."

The Bush administration has already heavily sanctioned Syria under the provisions of anti-terrorism laws, the Patriot Act and the Syria Accountability Act. Although no options have been taken off the table, the State Department emphasized yesterday that Washington is looking for a united international response. "We seek peaceful, negotiated diplomatic solutions," said spokesman Adam Ereli.

The report stirred drama yesterday as it became clear that a key passage had been edited at the last minute and that the names of Assad family members and Syrian officials had been deleted from the version released publicly.

The original report, which became public yesterday, included allegations that two family members and three top intelligence and security officials plotted the bombing of Hariri's entourage as it drove through Beirut, killing him and 22 others.

The document, compiled after a four-month probe by Mehlis, named Gen. Assef Shawkat, Assad's brother-in-law and the head of Syrian military intelligence, and Maher Assad, the president's younger brother. A witness told Mehlis's commission that the two men and the three others decided to kill Hariri two weeks after the passage of U.N. Resolution 1559 in Sept. 2004. The resolution, co-sponsored by the United States and France, called for an end to Syria's nearly three-decade-long occupation of Lebanon.

The original version of the report cited a witness who claimed that the five officials -- including Hassan Khalil, Bahjat Suleiman and Jamil Sayyed -- met several times in Damascus, including at Shawkat's office, over the next several months to complete the planning. The final meeting was in Shawkat's home less than two weeks before the attack, it said.

The version of the report distributed at the Security Council Thursday night excluded the names, referring only to senior Lebanese and Syrian officials.

Mehlis told reporters yesterday that the names were deleted after he learned his work was going to be made public. "No one outside of the report team influenced these changes, and no changes whatsoever were suggested by the secretary general or anyone at the U.N.," Mehlis said.

Syria's ambassador to Washington, Imad Moustapha, charged yesterday that the probe was based on "tales, innuendos" and did not contain a single substantiated piece of evidence that could be used in a court of law. "It is based on political attitudes, not fact," he said in an interview. "We ended up with a political report" laden with loopholes, contradictions and "shady testimonials" from witnesses who were not credible, he added.

Bolton dismissed the denial from Syria as "ridiculous."