The huge blast ripped through the seafront hotel district — an area that the billionaire businessman had helped to rebuild after the civil war — as his motorcade passed through.

His bodyguards were among the dead and Basil Fuleihan, a former Economy Minister, was critically wounded.

Mr Hariri, who had been Prime Minister for 10 years before standing down last October over a rift with Emile Lahoud, the pro-Syrian President, was returning from a meeting in parliament when the bomb went off.

At least 650lb of explosives were used to ensure that Mr Hariri’s heavily armoured car was destroyed. A 30ft-wide crater was left outside the badly damaged St George hotel. About 130 people were injured in the blast, mainly by flying glass. The bomb caused extensive damage for several hundred yards in every direction.

A previously unknown group, Jihad and Victory in Greater Syria, said that it had carried out what it claimed to be a suicide bombing and gave warning of further attacks against “infidels, renegades and tyrants”. However, suspicion fell on neighbouring Syria, whose 14,000 troops in Lebanon are becoming a contentious election issue.

Scott McClellan, the White House spokesman, said he was not blaming Syria, but that Lebanon should be able to determine its own course “free from violence, and intimidation and from Syrian occupation”.

Michael Young, an analyst, said: “Every way you look at this, it’s going to be a major blowback on Syria. Nobody is going to look anywhere else with seriousness.”

However, President Assad of Syria said he “condemned this horrible criminal action” and urged the Lebanese to reject those who plant “schism among the people” during this “critical situation”.

The Opposition issued a statement alleging that the Lebanese and Syrian governments were “fully responsible”. It called on the Government to resign and for Syrian troops to withdraw before May.

President Chirac of France, a close friend of Mr Hariri, called for an international inquiry.

As news of Mr Hariri’s death spread, demonstrators in his home town of Sidon in south Lebanon took to the streets chanting anti-Syrian slogans. “This is going to destabilise the country significantly for a long time to come,” a European diplomat said.

The Government declared three days of national mourning, during which all public or private institutions will stay closed. Lebanon’s army said last night it was on alert and set up checkpoints as patrols drove through the largely empty streets of central Beirut.

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