The findings and the reaction to them marked the latest escalation in tensions between the United States and Syria. US officials have accused Damascus of harboring terrorist groups and permitting fighters to cross into Iraq to attack US, Iraqi, and other forces there.

The report, issued Thursday to members of the UN Security Council, did not directly implicate President Assad of Syria, but said his government did not cooperate with the inquiry.

Bush spoke in California after helping dedicate a pavilion at the Ronald Reagan Presidential Library and Museum.

He said he had telephoned Secretary of State Condoleezza Rice earlier in the day and instructed her to call on the United Nations to convene a Security Council session ”as quickly as possible to deal with this very serious matter."

Bush was not specific about what steps the international community should take. He said the United States has started talking with UN officials and with Arab governments about that.

The United States and France are readying Security Council resolutions critical of Syria.

The Security Council, which can impose political and economic sanctions, was already scheduled to meet next Tuesday to consider the report from German prosecutor Detlev Mehlis. The US mission said yesterday that it had no plans to call for an earlier meeting time.

Separately, the UN will soon receive another report on Syrian compliance with last year’s UN demand that it quit Lebanon and allow political self-determination there.

Rice, on a trip to Tuscaloosa, Ala., said, ”Accountability is going to be very important for the international community."

Rice and British Foreign Secretary Jack Straw, with whom she was traveling, called on Syria to show good will toward Lebanon by establishing diplomatic relations with the country. Syria must ”fully understand" that it must not intervene in Lebanon and must respect its sovereignty, Rice said at a joint news conference.

The French government, which joined with the United States to pressure Syria to withdraw its troops from Lebanon, said it also was holding consultations in the UN Security Council.

The Mehlis report cited a witness who said Assef Shawkat, the president’s brother-in-law and Syria’s military intelligence chief, forced a man to tape a claim of responsibility for Hariri’s killing 15 days before it occurred. The report also said Syrian Foreign Minister Farouk al-Sharaa lied in a letter to the investigating commission.

Assad’s government repeated its claim of innocence in the Hariri killing and declared that the UN document was heavily politicized because of Syria’s staunch anti-Israeli position.