By Paul Reynolds
World Affairs correspondent, BBC News website
Whatever the motivation for the assassination of the former Lebanese Prime Minister Rafik Hariri, one of the effects is clear - the pressure is on Syria.
The claim of responsibility could well be a false trail
The United States, while not blaming Syria directly, has recalled its ambassador for consultations, a common way of displaying diplomatic displeasure.
At the moment, nobody seems to be taking too seriously a claim, backed by a videotaped statement, from an Islamist group saying that Mr Hariri had been killed as a "just punishment" for his close relations with Saudi Arabia, one of al-Qaeda's main targets.
An al-Qaeda link to the attack would have serious implications, but even if the cuplrits turn out not to be Syrian or Syrian-supported, such as Hizbollah, the heat will remain on Syria to withdraw its 14,000 troops from Lebanon.
It was Mr Hariri's opposition to those troops which many feel was the reason for the attack.
The presence of the troops has divided Lebanon and the death of Mr Hariri could be the spark which brings this issue to a head.
The United States certainly intends that this should be so.
UN resolution 1559
Washington will press for the implementation of Security Council resolution 1559 which was sponsored by the US and France and passed in September last year.
This called for the withdrawal of "all remaining foreign forces" from Lebanon.
A sign of US hostility to Syria came swiftly after the bomb. The White House spokesman Scott McClellan managed to mention Syria in the very first reaction by the Bush administration:
Some Lebanese see Syria as a hostile occupying power
"This murder today is a terrible reminder that the Lebanese people must be able to pursue their aspirations and determine their own political future, free from violence, and intimidation and free from Syrian occupation," he said.
This has to be seen in the wider context of US antipathy to the government in Damascus.
In his State of the Union speech this year, President Bush had harsh words for Syria: "We expect the Syrian government to end all support for terror and open the door to freedom," he said.
By "support for terror" Washington means alleged Syrian hospitality to the Palestinian militant groups Hamas and Islamic Jiyad as well as support for Hezbollah which still attacks Israel from southern Lebanon.
Mr Bush has not named Syria as a member of the "axis of evil" - that honour went to Iran, Iraq and North Korea, with Iraq having been retired from the club - but it does appear to be a candidate.
In May last year, Mr Bush banned US exports to Syria apart from food and medicine, stopped Syrian aircraft from flying to and from the United States and froze the assets of Syrians suspected of violating a law passed by the US Congress in November 2003.
This law, the Syrian Accountability and Lebanese Sovereignty Act, declared that its purpose was to "halt Syrian support for terrorism, end its occupation of Lebanon, and stop its development of weapons of mass destruction, and by so doing hold Syria accountable for the serious international security problems it has caused in the Middle East, and for other purposes."
The death of Hariri is sure to have deep repercussions
Other American accusations against Syria are that it has harboured Saddam Hussein supporters who are now fighting against US troops in Iraq and that it allowed insurgent fighters to cross its borders into Iraq.
Syria is still named as a "state sponsor of terrorism" by the State Department.
Syria is seen by the Bush administration as an obstacle to a settlement in the Middle East and as one of those country's in the region which is resisting democratisation.
So there is a long history to this and the death of Mr Hariri will only intensify American hostility.
For its part, Syria regards what happens in Lebanon as part of its own security.
It has announced moves to thin out its forces and move them further east towards its own borders.
The Syrian President Bashar al-Assad said of Mr Hariri's death: "Syria's government and people declare that they stand by brotherly Lebanon in these dangerous situations and extend the warmest condolences to the families of Rafik Hariri and the victims."
He described the apparent assassination as an "odious crime... aimed at striking Lebanese national unity and civil peace".
Syria resents and rejects all the American accusations, regarding itself as a true standard bearer of Arab unity and Palestinian interests.
The scene is set for a further deterioration of relations between Syria and the United States.