German prosecutor Detlev Mehlis, the chief of the probe, believes the Syrian silence has "considerably slowed down" the work of the commission investigating al-Hariri's death, Undersecretary-General for Political Affairs Ibrahim Gambari told the UN Security Council on Thursday.
After hearing Gambari's briefing, the council released a statement that urged all states to cooperate, "especially those who are yet to respond adequately".
That veiled reference to Syria had been more explicit in an earlier draft, but Russia and Algeria objected, council diplomats said.
President Emile Lahoud on Thursday accused some Lebanese groups of seeking to exploit the UN report to score domestic points, Aljazeera reported. He called on the Lebanese not to prejudge the investigation results.
UN representative in Beirut, Najib Friji, told Aljazeera that the procedural report was an interim one, in which Mehlis had submitted practical findings with a view to reaching the ultimate goal "that we hope is the truth".
Al-Hariri's killing led to change
of government in Lebanon
Speaking about the investigation report, Lebanon's communications minister, Marwan Hamadeh, told Aljazeera that "real clues have been found, which would lead to the revelation of at least part of the truth about the recurrent crimes".
US Ambassador John Bolton said the US was disappointed the Security Council couldn't have been more clear, and accused Syria of not cooperating.
"Let there be no ambiguity about the American view that Syria's lack of cooperation ... is not acceptable," Bolton said.
Earlier Aljazeera reported quoting sources in the UN that Mehlis was likely to request the Security Council for more time, after which he would submit his final report in accordance with Security Council Resolution 1595.
Al-Hariri's assassination in a 14 February 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.
"Let there be no ambiguity about the American view that Syria's lack of cooperation ... is not acceptable"
US Ambassador to UN
Syria withdrew the last of its troops in late April.
Lebanese opponents of Syria's role in their country accused Syria and its allies in the Lebanese security services of involvement in al-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 19 July request to interview five witnesses.
Nor had it responded to a request at the end of July for documents, he said.
Syria's UN Ambassador Fayssal Mekdad approached the UN on 18 August, 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.
Secretary-General Kofi Annan gave the probe a three-month mandate when it began its work on 16 June, but said it could be extended for three more months if Annan wants.