BEIRUT, Lebanon - Lebanese authorities have arrested a Sunni Muslim who according to a UN report telephoned President Emile Lahoud minutes before the murder of former premier Rafiq Hariri, officials said Sunday.

Mahmoud Abdel-Al, who is also member of the Islamic charity Al-Ahbache that is believed to have strong links with Syria, was arrested on Saturday on the order of the Lebanon's top prosecutor Said Mirza, judicial sources told AFP.

His detention is sure to ratchet up the pressure even more on the embattled pro-Syrian president, who has faced impassioned calls from opponents to step down ever since the murder of the five-time premier in a February bomb blast.

The arrest is the first to be made in connection with the murder since the report's publication on Thursday. However four other suspects, all seen as close to Lahoud, were arrested in August and are still in custody.

The move is the latest twist in a dramatic sequence of events after UN investigators probing the assassination implicated security officials in both Lebanon and Syria in their report.

Lahoud, a Maronite Christian, on Friday was forced to deny the claims in the UN report that he received a call on his mobile phone from Mahmoud Abdel-Al minutes before the bomb blast.

According to the UN report, Abdel-Al phoned Lahoud at 12:47 pm (1047 GMT) from his own mobile, just minutes before the blast, and followed this call up at 12:49 pm with one to Raymound Azar, the then head of Lebanese military intelligence.

Azar was arrested over the murder in August along with three other close aides of Lahoud -- presidential guard head, Mustafa Hamdan, former general security chief Jamil al-Sayed and ex-internal security head Ali al-Hage.

The report does not comment further on Abdel-Al's phone calls save to describe them as "interesting".

Mahmoud Abdel-Al is also the brother of a key suspect in the assassination, Ahmad Abdel-Al, who was in charge of public relations and information for the Al-Ahbache group. A third brother works for the presidential guard.

Ahmad Abdel-Al is named in the report as a key suspect who more "than any other figure is linked to the investigation". The report exhaustively details phone calls he made to Hamdan and other top security figures in the days leading up to the blast.

While Lahoud's office rapidly issued a statement after the report's release denying the president took a phone call from a suspect just before the murder, officials later acknowledged that someone had phoned one of the office's mobiles.

"A call was recorded on one of the mobiles in the service of the president of the republic ... but this call was not made with the president," a spokesman said.

US President George W. Bush has called the Mehlis report "deeply disturbing" and Secretary of State Condoleezza Rice called Sunday for firm United Nations action against Syria.

"It can't be ... just left lying on the table. It really has to be dealt with," she said in a joint interview with her British counterpart Jack Straw on BBC television.

Syria's highest political body, the National Progressive Front, meanwhile, rejected the UN report as distorted and deliberately aimed at damaging Damascus.

The report is "full of contradictions and has distorted the truth and the facts", said the Front, which groups eight parties headed by President Bashar al-Assad's Baath.

"The parties trying to harm Syria will use the political issues contained in the report ... which is based on testimony from people who lack all credibility," it said.

The Front also accused the UN special commission investigating the Hariri murder of having "distorted the testimony of Syrian officials" during interviews carried out last month.

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