Witness Hosam Taher Hosam appeared on Syrian state television last week and accused Lebanese officials, including Hariri's son Saad, of a scheme of threats, bribery and torture to induce him to falsely implicate Syria and said the initial findings of the U.N. inquiry rested largely on his lies.

Asked about Hosam's testimony, Saad al-Hariri told a media forum in Dubai: "There are people who have interest in trying to take the investigation to another level ... I never met him, I never had (any) connection with him. Definitely there were no bribes given to anybody in the investigation."

"He came to the commission freely and he then went to Syria freely...this is propaganda and part of the media campaign that some people are starting to undermine the (U.N.) commission."

U.N. investigators started questioning five Syrian officials in Vienna on Monday over Hariri's killing in Beirut, diplomatic sources said. Syria, which denies any role in the murder, agreed after guarantees from permanent U.N. Security Council member Russia that the officials could return to Damascus afterwards.

An interim report issued in October by the chief U.N. investigator, Detlev Mehlis, suggested the February 14 truck bombing that killed Hariri and 22 other people was planned by top Syrian security officials in Damascus and their Lebanese allies.

Mehils has said his inquiry had not been undermined by Hosam, dismissing his turnabout as propaganda.

The assassination of Hariri, a strong opponent of Syrian control over Lebanon, stirred an international outcry and weeks of Lebanese street protests that brought about Syria's pullout. It had sent forces into Lebanon in 1976 to quell a civil war.

Hariri, a member of parliament and his father's political heir, urged Syria to avoid procrastinating and cooperate with the U.N. investigation.

"The problem is between Damascus and the international community, nobody commits a crime and is above the law. We need to close this chapter quickly not to make it a political issue." (Reuters)