US President George Bush has said using force against Syria would be a "last resort" in the dispute over its alleged role in the death of Rafik Hariri.
Tens of thousands of Syrians held a protest against the UN report
He said he hoped Syria would co-operate with the UN inquiry into the killing.
A UN interim report on the killing of the former Lebanese prime minister implicated Syria and Lebanon - a charge both countries deny.
The UN Security Council is to discuss the report on Tuesday, and is expected to hear calls for action against Syria.
The report says the likely motive for Hariri's assassination was political - the former prime minister was increasingly at odds with pro-Syrian President Emile Lahoud at a time when Syria was the main power in Lebanon.
International pressure after his death led to Syria withdrawing its forces from the country.
The Bush administration believes the UN report gives it powerful leverage in stepping up the pressure on an Arab government to which it has long been hostile, the BBC's Middle East analyst Roger Hardy says.
Mr Bush said there needed to be "serious pressure" on Syria over the issues of insurgents crossing from Syria into Iraq, and its alleged support for Palestinian militant groups and interference in Lebanon.
"Nobody wants there to be a confrontation. On the other hand, there must be serious pressure applied," he said in an interview with the Dubai-based al-Arabiya television station.
KEY UN FINDINGS
Assassins had considerable resources and capabilities
Evidence suggests both Syria and Lebanon were involved
Crime was prepared over several months
Hariri's movements and itineraries were monitored
Highly unlikely Syrian or Lebanese intelligence were not aware of assassination plot
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"I am hoping that they will co-operate. It [military action] is the last - very last option.
"But on the other hand, you know - and I've worked hard for diplomacy and will continue to work the diplomatic angle on this issue."
Referring to a UN resolution calling on Syria to withdraw from Lebanon, he said: "I think one of the things that Syria has learned is that non-compliance with international demands will yield to isolation."
The Security Council is expected to hear from the report's author, the German prosecutor Detlev Mehlis.
His report said there was "converging evidence pointing at both Lebanese and Syrian involvement in this terrorist act".
The plot was complex and had obviously been planned for months, and as such it "could not have been taken without the approval of top-ranked Syrian security officials and could not have been further organised without the collusion of their counterparts in the Lebanese security services".
The report also said the Syrian authorities co-operated only to a degree and accused several interviewees of "trying to mislead the investigation". Syria says it co-operated with the inquiry.
No vote is expected at Tuesday's meeting, but the US, France and Britain are consulting other members on a possible future resolution calling for Syria to co-operate fully with Mr Mehlis' continuing investigation.