Charles Kennedy called on Tony Blair yesterday to use his special relationship with Washington to exercise a "cautionary tap on the shoulder" if necessary as the drive to wage war on terror continued.
The Liberal Democrat leader said that while there was a clear case for American military action, with feelings understandably running high, the US risked going too far.
"That's where a candid friend comes in. Standing shoulder to shoulder, but always there, for the occasional cautionary tap on the shoulder," he said. "The most special relationships, in my experience, are based on a combination of trust and mutual respect."
His speech echoed the growing concerns of party members at the extent of the military strikes and anti-terror laws being considered.
Delegates unanimously backed a motion calling for the military response to the crisis to be "precise and proportionate" and to avoid civilian casualties. They stood for two minutes' silence as a tribute to the victims of the terrorist attacks two weeks ago.
The opening debate of the conference was hastily rearranged to discuss the international crisis. Menzies Campbell, the party's foreign affairs spokesman, said any response to the atrocities should be based on "justice and not revenge". He told delegates: "The early chorus of condemnation will only be converted into a continuing coalition of support if the response is based on clear intelligence, is precise and proportionate to the need and is consistent with the principles of international law."
Delegates speaking during an hour-long debate warned against alienating the Arab world and called for international aid to help stem the growth of terrorism overseas.
Hughie Rose, a delegate from south London, told the conference: "I do not believe any casualties should be made and I don't believe we should go into any war. I don't believe Britain and America is in a moral position to be judge, jury and executioner."
Leaders of the official Iraqi opposition in Britain, however, claimed the strikes against the United States "bore the fingerprints" of Saddam Hussein and called for strikes against Baghdad as part of the military response to the attacks.
But Mr Kennedy warned there were clear limits to the support he would offer the Prime Minister and President George Bush, again insisting there could be "no blank cheque".
British troops should be used only if Britain was involved with the planning and risk assessment of any mission, Mr Kennedy said. And any new safeguards introduced in response to the attacks must not cut across fundamental civil liberties, he said.
Jenny Tonge, the party's international development spokeswoman, called for increased aid to be sent to Afghanistan to prevent the recruitment of further terrorists and called for protection for people caught up in potential strikes.
She said: "We must set up, if necessary, safe havens for those people until the threat of action subsides."
Lord Jacobs told delegates that the Islamic world should not forget the support of America for Muslims in Kosovo and Bosnia. America had supported the Egyptian economy with £2bn a year, he said.
Jonathan Fryer, a delegate from Leyton and Wanstead, warned that those who described America's war against terrorism as a "crusade" risked branding the action as a "medieval" action against Muslim "infidels".
He warned that an excessive response to the crisis could produce "repercussions that would make Pandora's box look like a Christmas stocking".
Susan Kramer, the former Liberal Democrat candidate for mayor of London, said: "We will not support a strategy of revenge and we will only support a strategy that focuses on the direct elimination of terror."Reuse content