“Let there be no ambiguity about the American view that Syria’s lack of cooperation … is not acceptable,” Bolton said.

Hariri’s assassination in a Feb. 14 bomb explosion as his motorcade was passing through central Beirut shook Lebanese politics. The blast, which killed 20 other people, triggered mass protests that brought down the pro-Syrian government two weeks later, and it increased international pressure on Syria to withdraw its troops from Lebanon. Syria withdrew the last of its troops in late April.

Lebanese opponents of Syria’s role in Lebanon accused Syria and its allies in the Lebanese security services of involvement in Hariri’s killing. Both authorities denied any involvement.

In his briefing to the council, Gambari said Mehlis’ probe had good cooperation from Israel and Jordan but that Syria had not answered a July 19 request to interview five witnesses. Nor had it responded to a request at the end of July for documents, he said.

Syria’s U.N. Ambassador Fayssal Mekdad approached the U.N. on Aug. 18 saying his country was willing to “engage in discussions,” Gambari said. But that offer can’t replace actual assistance, and Mehlis believes “the lack of timely response by the Syrian Arab Republic has considerably slowed down the commission’s work,” Gambari said.

In comments to reporters after Gambari’s briefing, Mekdad rejected the claim that Syria was slowing down the probe and said it wanted to cooperate.

“I would like to inform you that Syria is very much interested in all the results of the investigation,” he said. “We shall cooperate with Mr. Mehlis.”

Secretary-General Kofi Annan gave the probe a three-month mandate when it began its work on June 16, but said it could be extended for three more months if Annan wants.

Japan’s U.N. Ambassador Kenzo Oshima, Security Council president of August, said Mehlis was likely to request more time soon. Annan has said he would grant the request if Mehlis asks.