Lebanon ? Syria consented Monday to a U.N. investigator’s request to question top officials about the assassination of former Lebanese Prime Minister Rafik Hariri, a probe that increases the pressure on an increasingly isolated Damascus.

Investigator Detlev Mehlis took his expanded probe into Hariri’s Feb. 14 assassination to the Syrian capital for the first time, looking to interview top aides to President Bashar Assad.

Mehlis’ team already has accused four pro-Syrian Lebanese generals who controlled security in Lebanon at the time of Hariri’s death of involvement in the killing. Syria repeatedly has denied any role, but its opponents in Lebanon accuse it of ordering the slaying because Hariri had increasingly resisted Damascus’ control of Lebanon.

The German investigator’s visit Monday was logistical, aimed at securing Damascus’ cooperation and setting up a framework for the interviews. He was expected to return to Damascus next week, SANA said.

“An agreement was reached on measures and arrangements for meeting with Syrian witnesses,” the official Syrian news agency SANA said after Mehlis met with Riyadh Dawoody, a legal adviser and member of the Syrian Foreign Ministry’s political committee.