The United States, France and Britain challenged the rest of the UN Security Council to adopt a very tough resolution against Syria which would threaten sanctions if Damascus fails to cooperate fully with a UN investigation into the assassination of former Lebanese Prime Minister Rafik Hariri. Their tough draft resolution demands Damascus detain possible suspects and make them available to UN investigators, who have complained about Syria's cooperation. If Syria does not do this, the text says, the council would consider "further measures," such as economic sanctions, "to ensure compliance." The pressure on Syria is likely to intensify Wednesday when a report by the UN special envoy on Syria-Lebanon, Terje Roed-Larsen, on disarming Lebanese militias is released. There are allegations that Syria is continuing to smuggle arms to Palestinian militia groups in Lebanese refugee camps, in violation of a council resolution adopted in September 2004 demanding that all militias be disarmed. But how tough the Security Council will be on Damascus remains to be seen. Russia and China, which as permanent members 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. A draft resolution circulated late Tuesday by the United States, France and Britain strongly backs a report by the UN investigating commission which implicated top Syrian and Lebanese security officials in Hariri's assassination and accused Syria of not cooperating fully with the probe. US President George W. Bush made clear that America was now pursuing the diplomatic track and that military confrontation is only a last resort. Detlev Mehlis, the German prosecutor who heads the investigation team, urged Syria on Tuesday to cooperate better with his team to "fill in the gaps" about the organizers and perpetrators of the February 14 assassination. Mehlis addressed the Security Council five days after issuing a report implicating top Syrian and Lebanese officials of orchestrating the bombing that killed Hariri and 20 others. The report said Syria's cooperation with the investigation in form but not in substance "impeded the investigation and made it difficult to follow leads." To complete the probe, the Syrian government must fully cooperate with investigators, including by allowing Syrians to be interviewed alone outside Syria, it said. Mehlis' investigation has been extended until December 15 and he told the council his team would reinterview a number of witnesses, interview new ones, complete its examination of recently obtained evidence and cooperate with Lebanese judicial and security authorities. In an interview on Al-Arabiya hours before the Security Council met, Bush made clear that the US prefers the diplomatic track and said that military action against Syria is not on the table at this time. "It is the last - very last option. And no commander-in-chief likes to commit the military, and I don't. But on the other hand, you know - and I've worked hard for diplomacy and will continue to work the diplomatic angle on this issue," he said. Later, in a speech, Bush stressed the need to make those responsible for Hariri's death accountable for their actions and called Syria a destabilizing force in Lebanon. "Syria and its leaders must be held accountable for their continuing support of terrorism, including any involvement in the murder of prime minister Hariri," he said. The investigating commission also believes the extended investigation "would provide yet another opportunity for the Syrian authorities to show greater and meaningful cooperation, and to provide any relevant substantial evidence on the assassination." "For this reason, the Syrian authorities may wish to carry out on their part their own investigation into the assassination of Mr. Hariri in an open and transparent manner," Mehlis said. "This would enable the commission to fill in the gaps and to have a clearer picture about the organizers and perpetrators." For such a complex case as the Hariri assassination, Mehlis added that it would be entirely normal for the investigation to take "many months, if not years... to cover all aspects of investigation with certitude and to prepare a case for prosecution." He called for stepped up security for his team of 30 investigators from 17 countries, saying the already high risk the team faced is certain to increase following the report. He added that "the commission has received a number of threats which were deemed, in the assessment of our security personnel, to be credible." Syria's UN Ambassador Fayssal Mekdad said every paragraph in the Mehlis report deserved to be refuted and criticized Mehlis for accusing Syria before the end of the investigation, saying the commission "should not have pointed the finger or cast doubt on anybody. Mehlis's findings brought swift denials from the Syrian government, which called the report biased, politicized and an American plot to take over the region. "Syria has cooperated faithfully and sincerely with the Independent International Commission," Mekdad told the council. "Syria will continue its cooperation..." Boutros Assaker, the acting secretary-general in Lebanon's Foreign Ministry, called on "all concerned parties to sincerely and effectively cooperate" with the Mehlis inquiry so it can obtain "the complete and absolute truth and the punishment of all the criminals and the murderers, wherever they are." The US administration is talking about Monday as a target date for a resolution - and a ministerial meeting of the Security Council to give its adoption added prominence. But Russia and China - both veto-wielding members of the council - don't appear in any hurry, and Moscow, which has close ties to Syria, would likely oppose sanctions or any reference to them. "My government is always very cautious with such sensitive issues as Syria-Lebanon," Russia's UN Ambassador Andrey Denisov said Monday. Russia's Foreign Ministry spokesman Mikhail Kamynin warned in a statement Saturday that "the settlement of this problem should in no way lead to the emergence of a new hotbed of tension and further destabilization in the Middle East." China's UN Ambassador Wang Guangya told reporters, "We are still studying the report so I don't want to make any comments now... It needs careful study." Algeria's UN Ambassador Abdallah Baali, the only Arab member of the Security Council, said "obviously, everybody has to cooperate with the commission in order to get the whole truth and so this applies to all concerned including Syria." But he indicated it was too early to envisage "any action, or any kind of measures." Asked about sanctions as he left the council's closed-door discussion following Mehlis's public briefing, Secretary-General Kofi Annan said "what is important is that... everyone cooperates with Mehlis so that we can get to the truth." "We also have to understand that after this, there will be a judicial process, and we should be careful not to do anything that interferes with the judicial process or the rights of the accused," he warned. AP contributed to this report.