Syria's President Bashar al-Assad has agreed to meet the chief United Nations investigator probing last year's killing of Rafiq Hariri, Lebanon's former prime minister.

The meeting, which will take place in the next few weeks, could help to lift immediate international pressure on the Syrian regime but will also inject fresh momentum into the UN inquiry.

A progress report released yesterday by Serge Brammertz, the Belgian prosecutor leading the investigation, said Damascus had improved its co-operation with the inquiry.

Following months of foot-dragging and obstruction, Syria has signalled that it will comply with any request for the arrest of individuals and has provided documents the UN commission investigating the death had requested.

Mr Brammertz took over from Detlev Mehlis, the German prosecutor, three months ago and has been rebuilding the commission, most of whose members have also departed.

He has also been reviewing the evidence so far gathered to try to build a case that would stand up in an international tribunal. Adopting a more secretive and low-key approach, he said yesterday he had made progress but refused to name suspects.

Previous interim reports by Mr Mehlis had implicated high-level Lebanese and Syrian officials in the February 14 2005 assassination, and raised questions about Mr Assad's own role. Mr Mehlis had asked to interview the Syrian president to discuss allegations that he had threatened Hariri with physical harm in a meeting in Damascus in 2004.

Mr Assad denies Syrian involvement in the assassination, but he had, until now, resisted requests for an interview.

Western diplomats say Mr Brammertz is working under the same hypothesis as Mr Mehlis but they suggest he needs to gather more solid evidence before bringing any Syrian officials to trial.

The prospects of a more prolonged inquiry, say diplomats, and the departure of Mr Mehlis (for what he said were personal reasons), have given confidence to the authorities in Damascus. More pressing regional concerns, namely the controversy over Iran's nuclear programme and the Palestinian election victory of the Islamist Hamas group, have deflected international attention away from Syria.

The UN report comes as rival Lebanese political factions yesterday failed to agree on how to remove pro-Syrian President Emile Lahoud from office but pledged to resolve the crisis when a "national dialogue" conference resumes on March 22.

International pressure forced Damascus to pull its military forces out of Lebanon in the aftermath of the Hariri killing, ending a nearly 30-year presence. But Syria still has allies in Beirut, including Mr Lahoud and two parties representing the Shia Muslim community.

Anti-Syrian politicians, led by Saad Hariri, the killed leader's son, had given Mr Lahoud until yesterday to resign in the face of a popular uprising, but they are now trying to resolve the dispute over the presidency through the "national dialogue".