President Bush said today that military action was a "last resort" in dealing with Syria if Damascus refused to co-operate with a United Nations investigation into the murder of Rafik Hariri, the former Lebanese prime minister.

The UN Security Council is due to be briefed tonight by Detlev Mehlis, the German prosecutor whose report last week found evidence of high-level Syrian involvement in the bombing that killed Mr Hariri and 20 others in Beirut in February.

US and French diplomats in New York are leading the drive to have a strongly worded resolution passed by the council next week calling on Syria to co-operate fully with the Mehlis probe.

"A military (option) is always the last choice of a president," Mr Bush told al-Arabiya television in an interview broadcast today. "I am hoping that they will cooperate. It is the last -- very last option... I’ve worked hard for diplomacy and will continue to work the diplomatic angle on this issue."

Although Russia, which has close ties to Syria, has warned about the risk of destabilising the Middle East, Washington and Paris quickly joined forces to back Herr Mehlis's report last week after it found evidence of Syrian involvement in the assassination and a lack of cooperation from Damascus.

Herr Mehlis is due to brief the Security Council this morning, New York time, and Lebanon and Syria have also asked to speak, although no draft resolution has yet been circulated.

On a visit to Canada, the US Secretary of State, Condoleezza Rice, urged Syria to drop its "nonchalant attitude" about the report's findings, and John Bolton, Washington's ambassador at the UN, demanded that Syria co-operates with the investigation.

"This is true confessions time now for the government of Syria," Mr Bolton said. "No more obstruction. No more half measures. We want substantive cooperation and we want it immediately."

In his interview with al-Arabiya, a transcript of which was obtained by Reuters, Mr Bush said Syria had to meet a set of demands from the international community, including expelling Palestinian militant groups, preventing insurgents from crossing its borders into Iraq to fight US forces, and ending Syrian interference in Lebanon.

"Nobody wants there to be a confrontation. On the other hand, there must be serious pressure applied," he said.

"In other words, there are some clear demands by the world. And this report, as I say, had serious implications for Syria, and the Syrian government must take the demands of the free world very seriously."

Hariri and 20 others were killed on February 14, prompting mass demonstrations that eventually forced Syria to withdraw its forces from Lebanon.

The UN report said that the decision to kill him "could not have been taken without the approval of top-ranked Syrian security officials" colluding with counterparts in Lebanon. Syria has vigorously denied the accusations.

Mr Bush would not be pinned down on what action Washington would take if Syria does not comply. "I certainly hope that people take a good look at the Mehlis report ... there’s clear implications about Syrians' involvement in the death of a foreign leader," he said.

"The United States was willing to help, work with other countries, and we will, to make sure that out of the United Nations comes a clear message."

Asked if the United States would support a call by Hariri’s son, Saad, for an international court to try his father’s killers, Mr Bush said the decision lay with the United Nations. "Well, we want people to be held to account. And I’d be glad to talk to other leaders to determine whether or not that’s the best course of action. But certainly, people do need to be held to account. And the first course of action is to go the United Nations," he said.

The Bush Administration is talking about next Monday as a target date for a resolution - and a ministerial meeting of the Security Council to give its adoption added prominence.

But Russia and China - both veto-wielding members of the Council - do not appear in any hurry, and Moscow would oppose sanctions or any reference to them.

Russia’s Foreign Ministry spokesman, Mikhail Kamynin, warned in a statement on Saturday that "the settlement of this problem should in no way lead to the emergence of a new hotbed of tension and further destabilisation in the Middle East".

Kofi Annan, the UN Secretary-General, has extended the Mehlis investigation until December 15 and made clear yesterday that it was just the beginning of a legal process.

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