UN investigators probing former Lebanese prime minister Rafiq Al Hariri's killing cannot question Syrian President Bashar Al Assad, Damascus said yesterday.

But Information Minister Mahdi Dakhl-Allah said Syria would still co-operate with the inquiry.

The UN Security Council has threatened Syria with "further action" if it did not fully co-operate with the inquiry into the February 14 assassination of Hariri in a Beirut truck bombing.

Asked if Syria rejected a meeting between Assad and the investigators, Dakhl-Allah told Egyptian radio: "Certainly, because the issue is related to Syria's sovereignty. Syria is committed to its independence and sovereignty."

Sources familiar with the inquiry said it would question four Syrians, including the former chief of intelligence in Lebanon Lieutenant General Rustom Ghazali, in Vienna on Monday.

Investigators had already questioned him and identified him as a suspect.

The four also include Hosam Hosam, a witness who had implicated Syrian officials in the assassination but who later fled Beirut for Syria, where he said his accusations were false.

The inquiry team requested last month to interview Assad, his foreign minister, Farouq Al Shara, and other officials. Diplomats have said Syria has indicated Shara will be allowed to meet the inquiry.

Meanwhile, the new chief of the UN probe, Belgian prosecutor Serge Brammertz, is to take up his post in Beirut next week. "We are expecting Mr Brammertz next week in Beirut," where the investigative commission is based, spokeswoman Nasrat Hassan said. "But we don't yet know the exact day of his arrival."

PHOTO CAPTION

Syria's President Bashar al-Assad (L) and the then Syrian Vice President Abdel-Halim Khaddam in a June 6, 2005 file photo. (REUTERS)