The United States, France and Britain have challenged the rest of the U.N. Security Council to adopt a tough resolution threatening sanctions against Syria if it doesn't cooperate fully with a U.N. investigation into the assassination of former Lebanese prime minister Rafik Hariri (search).

The pressure on Syria is likely to intensify Wednesday when a report by the U.N. special envoy on Syria-Lebanon, Terje Roed-Larsen (search), on disarming Lebanese militias is released.

There are allegations Syria is continuing to smuggle arms to Palestinian militia groups in Lebanese refugee camps, in violation of a council resolution of September 2004 demanding that all militias be disarmed.

But Russia and China, which have veto power, and Algeria, the only Arab member of the council, have been hesitant to use the threat of sanctions to back up a call for more Syrian cooperation.

Russia on Wednesday signaled it would not allow sanctions against Syria.

"Russia opposes sanctions against Syria," spokesman Mikhail Kamynin said while accompanying Foreign Minister Sergey Lavrov (search) on a trip to Israel, according to the Interfax, Itar-Tass and RIA Novosti news agencies. "Russia will be doing everything necessary to prevent attempts to impose sanctions against Syria."

A draft resolution circulated late Tuesday by the United States, France and Britain strongly backs a report by the U.N. investigating commission that implicated top Syrian and Lebanese security officials in Hariri's assassination and accused Syria of not cooperating fully with the probe.

The report brought swift denials from the Syrian government, which called it biased, politicized and an American plot to take over the region.

Syria's U.N. Ambassador Fayssal Mekdad (search) told the council that every paragraph in the report deserved to be refuted. He insisted Syria "has cooperated faithfully and sincerely" and will continue to do so.

If adopted, the draft resolution would require Syria to detain anyone the U.N. investigators consider a suspect and allow the individual to be questioned outside the country or without Syrian officials present. It would also immediately freeze the assets and impose a travel ban on anyone identified as a suspect by the commission.

The language appeared to be an effort to pressure Syria into giving the investigators access to top security officials — possibly including the brother-in-law and brother of President Bashar Assad (search) — who may be implicated in Hariri's slaying.

Syria would also be required to renounce terrorism and "commit itself definitively to cease all support for all forms of terrorist action and all assistance to terrorist groups and to demonstrate this undertaking through concrete actions."

If Syria does not fully cooperate with the investigation, the draft says the council intends to consider "further measures," including sanctions, "to ensure compliance by Syria."

"We want a very strong signal to the government of Syria that its obstruction has to cease and cease immediately," U.S. Ambassador John Bolton (search) said.

President Bush insisted Tuesday that the United Nations hold Syrian leaders "accountable for their continuing support of terrorism."

But Russian President Vladimir Putin (search), in a phone conversation Tuesday with Assad, welcomed Syria's stated willingness to cooperate with the investigation and emphasized that the council must proceed carefully.

The two discussed the "urgent need for cautious action by the international community in order to prevent the emergence of new sources of tension in the region," the Kremlin said in a statement.

Russia and China have expressed concern about any actions that might destabilize the Middle East.

Council experts are expected to discuss the resolution over the next few days and Bolton said ministers from the 15 council nations will likely come to New York on Monday, hopefully to adopt it. Diplomats said a ministerial meeting would add clout to the resolution and increase pressure on Syria.

German prosecutor Detlev Mehlis (search), who is leading the U.N. probe, urged Syria earlier Tuesday to help "fill in the gaps" about who orchestrated the car bombing that killed Hariri and 20 other people in Beirut on Feb. 14.

"I cannot send 500 investigators, which I do not have, to Syria to look for documents because I do not know where I would find them," he told reporters. "It would be a good idea if the Syrian authorities made an extra effort by themselves."

Mehlis has received an extension of his mandate until Dec. 15, which he told the council offers "yet another opportunity for the Syrian authorities to show greater and meaningful cooperation."

The draft resolution asks Mehlis to report on the progress of his inquiry and Syrian cooperation by Dec. 15, or earlier if it isn't getting sufficient cooperation.

Mehlis requested stepped up security for his team of 30 investigators from 17 countries.

The commission has received threats, he said.