The United Nations Security Council today passed a resolution ordering Syria to co-operate with the investigation into the murder of former Lebanese prime minister Rafik Hariri - or face "further action".

The resolution orders Damascus to arrest and freeze the assets of anybody the UN suspects of involvement in the killing. It was passed unanimously.

Although no Syrian officials have yet been designated as suspects in the Hariri murder, a UN inquiry led by Detlev Mehlis, a German prosecutor, has implicated President Bashar Assad’s brother and brother-in-law, as well as the former heads of military intelligence and internal security.

Condoleezza Rice, the US Secretary of State, warned Syria of“serious consequences” if it refuses to co-operate, and said Damascus must now “make a strategic decision to fundamentally change its behaviour.”

“With our decision today, we show that Syria has isolated itself from the international community through its false statements, its support for terrorism, its interference in the affairs of its neighbours, and its destabilising behaviour in the Middle East,” she said.

As a concession to China and Russia, which had promised to veto any direct threats against Syria, the resolution stops short of threatening economic sanctions against Syria if Mr Assad refuses to comply.

"Syria must detain those Syrian officials or individuals whom the commission considers as suspected of involvement in the planning, organisation, sponsoring, organising or perpetrating of this terrorist act, and make them fully available to the commission," the resolution said.

The text also establishes a sanctions subcommittee, which will allow Russia to use a procedural device to block any travel or financial measures against Syrian officials.

One witness cited in the UN report has charged that Mr Assad’s brother, Maher, and his brother-in-law, Assef Shawkat, were involved in the assassination of their Lebanese enemy, who was killed along with 20 other people in an explosion in Beirut on February 14.

The resolution, which was was passed under Chapter VII of the UN Charter, which allows for the use of force in last resort, also ordered Syria not to meddle in the domestic affairs of Lebanon. Syria withdrew its soldiers from Lebanon after a 29-year presence in the country in April.

"Syria must not interfere in Lebanese domestic affairs, either directly or indirectly, refrain from any attempt aimed at destabilising Lebanon, and respect scrupulously the sovereignty, territorial integrity, unity and political independence of this country," said the text.

Jack Straw, the Foreign Secretary, said that the Security Council was "putting the Government of Syria on notice that our patience has limits".

"The people of the Lebanon have become all too acquainted with grief," he said. "We owe them a better future and this resolution is one way of providing them with that better future."

Dr Rice said that today's resolution was the only way to strengthen the Mehlis commission, which has complained that Syria is blocking its inquiries.

"Syria has offered no truthful explanations to these serious allegations," said Dr Rice. "Instead it has chosen until now to dismiss the commission report as politically motivated.

"The Chapter VII resolution that we are passing today is the only way to compel the Syrian government to accept the just demands of the United Nations and to co-operate fully with the Mehlis investigation," Dr Rice told the Security Council.

Syria, which denies any complicity in the murder of Mr Hariri, has spent the last few days reaching out to Arab leaders in the face of pressure from the Bush Administration and European leaders. On Saturday, Mr Assad said he would launch a Syrian investigation into the assassination.

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