"We consider the resolution to be very negative towards Syria, and as it is unanimous this makes it more problematic," a Foreign Ministry source said of Monday's Security Council vote.
"It is accusatory and adopts the assumptions that (chief UN investigator Detlev) Mehlis had arrived at which we consider hasty and not objective enough," the source said.
Mehlis, the German prosecutor conducting the inquiry, has pointed to Syrian security officials as suspects in the February 14 Beirut bombing that killed Hariri and 22 others.
His October 20 report spoke of "converging evidence" of Syrian and Lebanese involvement in Hariri's killing and said it would be hard to imagine how such a plot could have gone ahead without the knowledge of Syrian and Lebanese intelligence services.
Tightening the diplomatic noose around Syria, US Secretary of State Condoleezza Rice told the council that the resolution "made it clear that failure to comply with these demands will lead to serious consequences from the international community".
But unanimity was achieved only after the United States, France and Britain, sponsors of the resolution, agreed to drop an explicit threat of economic sanctions against Syria. Otherwise Russia, China and Algeria might have abstained.
Instead, the resolution says the council "could consider further action" if Syria fails to meet demands that include detaining anyone whom Mehlis wants to question.
PROTEST On Tuesday, several hundred Syrians waved flags and sang nationalist songs outside the US embassy in Damascus to protest against the resolution, which Syria dismisses as politically motivated.
Damascus has denied any role in Hariri's murder.
"We have come here because our hearts are with Syria in these difficult times. We want to raise our voices against American intimidation and bullying," protester Madda Mughrabi said.
In Lebanon, President Emile Lahoud, a staunch Damascus ally, said in a statement he hoped the resolution would uncover the "whole truth" and provide "solid evidence that points to the planners, executors and those who helped carry out the crime".
Lahoud has maintained that Syria and its Lebanese allies were not linked to the murder and a thorough investigation would reveal their innocence.
RUSSIA DEFENDS STANCE:
Russia defended its stance at the United Nations, saying it had spared Damascus the threat of sanctions and of being linked, without proof, with terrorist activities.
A statement by the Russian Foreign Ministry said: "Thanks to the efforts of the Russian side and other delegations, politicised stances that had nothing to do with the investigation of Hariri's death were withdrawn."
Russia, an ally of Syria since Cold War times, said the resolution, as passed, opened the way for "broad and effective dialogue of the Syrian side with international investigators".
GERMANY WELCOMED DECISION:
In Berlin, German Foreign Minister Joschka Fischer welcomed the resolution as well as the UN decision to extend the mandate of the investigating commission to December 15.
"It is now up to all countries - above all Syria - to immediately, completely and comprehensively cooperate with the investigating commission. The statements of the Syrian government that it would cooperate with the commission mus now be followed by deeds," Fischer said in a statement.
Mehlis returned to Beirut hours after passage of the resolution, which also orders Damascus to give investigators complete access to places, documents and people.
An unedited version of Mehlis's report named as suspects two close relatives of Syrian President Bashar al-Assad - his brother Maher al-Assad, a key military commander, and Assef Shawkat, his brother-in-law and military intelligence chief.
The death of Hariri, an opponent of Syrian domination of his country, transformed Lebanon's political landscape.
The killing led to a pullout of Syrian troops from Lebanon after three decades and has piled pressure on Damascus, which Washington accuses of aiding insurgents in neighbouring Iraq and of undermining Middle East peace efforts.