Syrian authorities have begun investigating the death of Ghazi Kanaan, powerful interior minister and the Syrian government's key man in Lebanon for two decades, who reportedly committed suicide on Wednesday.
Damascus has condemned any suggestion of foul play in the death of Kanaan, its former security chief in Lebanon.
Kanaan is said to have shot himself at his Damascus office.
Washington described Kanaan as a "central figure in Syria's occupation of Lebanon for many years" but declined to comment on the circumstances of his death, reports BBC.
Two officials familiar with the international investigation said they had their doubts that Mr. Kanaan's death was a result of suicide.
"We are not really surprised that something like this had happened," said one of the officials. "But we are only surprised by who it was." Both spoke on condition of anonymity.
But an American official in Washington, also requesting anonymity, said: "From what I've seen, there is no indication that it was not suicide. But deaths of this kind are bound to be manipulated to the high heavens."
Mr. Kanaan was visibly under strain in recent months, as international pressure bore down on him and the government after Mr. Hariri's killing. In an interview with Voice of Lebanon radio on Wednesday morning, just hours before his death, he sounded emotional.
"I want to make clear that our relation with our brothers in Lebanon was based on love and mutual respect," he said, his voice cracking at times. "We have served Lebanon's interest with honor and honesty."
Then, just before concluding, he added tersely, "I think this is the last statement I will give."
The most immediate impact of Mr. Kanaan's death is likely to be on the United Nations investigation led by Detlev Mehlis, a German prosecutor. He is expected to present a preliminary report to the Security Council on Oct. 25, but has also been asked to continue working through mid-December, imforms the New York Times.