The United States and France say they expect the Lebanese government to keep its promise and cooperate fully with a new international investigation into the assassination of former Prime Minister Rafik Hariri (search).

France's U.N. Ambassador Jean-Marc de La Sabliere told reporters that Thursday's unanimous Security Council approval of a resolution authorizing the investigation underlined how strongly the council "wants the truth to be established."

The council's 15-0 vote came two weeks after a U.N. fact-finding team issued a report saying a Lebanese investigation was riddled with flaws and didn't meet international standards. The team, led by deputy Irish police commissioner Peter Fitzgerald, said an international probe was needed.

Hariri's Feb. 14 killing in a bombing caused an uproar in Lebanon, sparking massive anti-Syrian street protests. The Lebanese opposition claimed Syria and Lebanon's pro-Syrian government orchestrated the killing. Syria denies any involvement.

"We want to get to the bottom of this assassination and what we believe to be a terrorist act," U.S. deputy ambassador Stuart Holliday said. "Lebanon has indicated they will cooperate. We expect them to hold to their word, and that includes all aspects of the government of Lebanon."

The resolution welcomes Lebanon's approval of the independent investigation, but the council rejected amendments proposed by the government that would have given it a major role in the inquiry.

The council authorized a commission to assist Lebanese authorities in their investigation "of all aspects of this terrorist act," but it left the commission to decide what role Lebanese authorities play.

Lebanese authorities should give investigators access to all documents and evidence in their possession, it said. The resolution also gives the commission authority to collect any additional information and evidence, visit any relevant sites, and "interview all officials and other persons in Lebanon that the commission deems relevant to the inquiry."

Council members, however, were reluctant to say whether this meant the investigators could have access, for example, to the presidential palace or to interview Lebanese President Emile Lahoud (search).

Holliday responded by reiterating Lebanon's pledge to cooperate and added, "We would be surprised if they did not honor their commitment to cooperate."

The resolution — co-sponsored by the United States, France and Britain — urges the independent commission to complete its work in three months but gives Secretary-General Kofi Annan (search) authority to extend its mandate for an additional three months.

Russia, China and Algeria wanted to make sure that the resolution reaffirmed Lebanon's sovereignty while giving the probe enough independence to be effective.

"I think the important thing for this resolution is that ... this commission has to cooperate and work within the framework of Lebanese laws and their legal systems," said China's U.N. Ambassador Wang Guangya, the current council president.

The size of the commission hasn't been determined, though the authors of the Fitzgerald report had recommended a group of 50, acting U.S. Ambassador Anne Patterson said Wednesday.

She said the mission would include experts focused solely on explosives, forensics or other highly technical fields.

The international outcry over Hariri's assassination forced Damascus to begin withdrawing its army from Lebanon after nearly three decades of dominating the neighboring country. Syria has said all its troops and intelligence agents will be out of the country by the end of April.