NEW York - A top UN investigator reported Thursday that he had made progress in establishing the motives for the assassination of former Lebanese prime minister Rafik Hariri and linking them to suspects in the killing. Serge Brammertz, who heads the international commission investigating Hariri's murder on February 14, 2005, said substantial facts had been uncovered and "valuable links within and between the main components of the case" had been made by his team of investigators.

The massive bomb explosion killed Hariri and 22 other civilians. Brammertz is also investigating the political murders of at least 15 Lebanese journalists and politicians, who like Hariri, had opposed Syrian military occupation of their country.

"The aim remains to link together the most responsible perpetrators with others who knew about the crime, those who participated in the execution of it, and those who assisted in the preparation of the necessary components for its execution," Brammertz said in a progress report to the UN Security Council. Thursday's report was the seventh since May, 2005, when the investigation was ordered.

Brammertz said Lebanon, Syria and other states have provided "mostly positive and timely responses" to requests for assistance in the investigation. But he said the current volatile political and security environment in Lebanon, and the lack of qualified staff, have had an impact on the work of investigators.

He said he had requested interviews with Syrian officials and groups, and Damascus had met those demands "within the appropriate timescales" and he was grateful for the logistical and security arrangements provide by Syria.

"The commission will continue to request Syria's full cooperation, which remains crucial to the swift and successful completion of the commission's mandate," Brammertz said.

Brammertz, of Belgium, is a former prosecutor of the International Criminal Court. He has been cautious in revealing more details of the investigation.

Hariri's murder led to massive street protests in the so-called Cedar revolution that ousted the pro-Syrian government. Months later, Syria responded to intense international pressure to withdraw its troops that had occupied the country for decades after the Lebanese civil war. -DPA