Chief UN investigator Detlev Mehlis returned to Lebanon on Tuesday to continue his probe into the murder of former Lebanese Prime Minister Rafik al-Hariri, a UN official based in Lebanon told reporters.

Mehlis, a German prosecutor who heads the UN investigation into the Feb. 14 truck bomb assassination of al-Hariri and 20 other people in Beirut, has until Dec. 15 to report back to the UN Security Council on his findings about the assassination of Hariri.

He has demanded he be allowed to question six top Syrian military and intelligence officials over the murder at his headquarters in Lebanon.

He has also been waiting for the full cooperation of Syria since the Security Council adopted a resolution last month demanding Syria's full and unconditional cooperation and warning further action against Damascus if it does not do so.

Mehlis held talks with a Syrian official in Spain last week but could not agree on a venue to question the six top Syrian officers. Mehlis has insisted on questioning the six Syrians in Lebanon -- where he has the power to detain suspects -- but Syria has refused.

The six Syrian officials include Syrian President Bashar al-Assad's brother-in-law and head of Syrian military intelligence, Major General Assef Shawkat.

UN Secretary-General Kofi Annan made calls last week to President Assad to seek agreement on a location where Mehlis could question the officials.

Mehlis rejected the proposal by Syria that he use UN offices in the Golan Heights. Discussions on a venue in a third country are continuing.

In an interim report last month, Mehlis implicated senior Syrian and Lebanese officials in the murder of Hariri, but Syria has denied any role.

Source: Xinhua