A U.N. team probing the assassination of Lebanon's former prime minister found that some of his killers were probably terrorists, and said Tuesday that Syria's president has agreed for the first time to meet with investigators.

The meetings, expected later this month, would mark a significant reversal for President Bashar Assad and Vice President Farouk al-Sharaa, who have steadfastly refused to heed interview requests.

The probe has repeatedly accused Damascus of failing to cooperate in the investigation into the slaying of former Lebanese Prime Minister Rafik Hariri.

The report was released by the U.N. investigating commission's new chief Serge Brammertz.

U.N. investigators had earlier implicated top Syrian and Lebanese officials in the explosion that killed Hariri and 22 others on Feb. 14, 2005. Among those linked to the killing was Brig. Gen. Assaf Shawkat, Syria's military intelligence chief and Assad's brother-in-law.

Brammertz's predecessor repeatedly accused Damascus of failing to cooperate in the Hariri investigation.

"The individuals who perpetrated this crime appear to be very 'professional' in their approach," the report said. "It must be assumed that at least some of those involved were likely experienced in this type of terrorist activity."

Brammertz, who took over the investigation in January, wrote in the report to the U.N. Security Council that his commission had reached a deal for extensive Syrian cooperation. He said Syria had signaled that it might arrest those his team suspects of involvement, a request it had previously resisted.

"This understanding will be tested in the upcoming months," Brammertz wrote.

Syria has denied involvement in Hariri's death. The assassination led to demonstrations against Syria's decades-long dominance of Lebanese affairs and magnified international pressure on Damascus to withdraw its troops, which it eventually did.

In his report, Brammertz said investigators still had no unifying theory about how the blast was executed, but that the team knew more now about how conspirators prepared the plot. Much of his work in recent weeks was spent analyzing evidence collected by his predecessor, Detlev Mehlis.

Noting the complex nature of the plot to kill Hariri and the discipline and skill required of those who carried it out, the report speculated that at least some of those involved had been involved in terrorist acts before.

According to the report, 10 people are still in custody in connection with Hariri's slaying.

Brammertz' report was intentionally short on specifics, a distinctive shift in tone from Mehlis' two reports, which exhaustively detailed the evidence suggesting Syrian and Lebanese involvement in Hariri's killing.

Brammertz wrote in the final paragraph of his report that he understood his secrecy might prove limiting. Yet he said caution was crucial, "and indeed, is standard investigation practice."

The Security Council had also charged Brammertz' commission with providing technical assistance to investigations into 14 other bomb blasts in Lebanon since Oct. 1, 2004.

The report said it was too early to draw any link between the 14 bombings or to say if they were connected with Hariri's slaying. However, it did say that the lack of progress so far in investigating the bombings "appears ... to strain the confidence in, and trust between, the judiciary, the various security forces, the families of the victims, and the public in general."