Charles Kennedy has pledged his party's support for Britain's troops in the Gulf.

The Liberal Democrat leader, in a keynote speech on Thursday, said his party now has a duty to back British troops.

"The House of Commons has sanctioned British involvement. Our duty now is clear: to support our armed forces, and to hope that any military conflict is swift and successful for our troops, with the minimum loss of life on all sides," he said.

Kennedy, in the final of three speeches on wider policy issues for the party, warned that government planners would have to give more time to the humanitarian effort.

"There is an urgent need to consider the aftermath of any action. Saddam Hussein has abused human rights over many years. He has not only tortured and killed many of his own people. He has also reduced them to abject poverty.

"We must ensure that military action does not make all these problems worse," he said.

Kennedy said he is "not convinced" that there is a viable humanitarian plan in place for Iraq.

He argued that the UN should be allowed to take over ensuring food and medical supplies reach the people who need them, partly as a way of repairing the damage caused by the failure of the Security Council to agree.

"The decision of the United States to take unilateral action has dangerously undermined the international order. There is an urgent need for the UN to start repairing the damage.

"And by spearheading the humanitarian effort in Iraq, it may begin not only to help the Iraqi population but also to restore faith in the most important of all our international organisations," he said.

He warned that the rows at the UN have left the organisation "at a critical point in its history".

"It is the US, stung by the events of September, which is challenging the boundaries of international law," he said.

"We must work to keep the USA engaged in the United Nations and to make the UN stronger and more effective."

Highlighting wider issues of internationalism, Kennedy argued that Britain needs to be at the heart of Europe in order bring forward reform on issues like CAP.

Kennedy also claimed that Labour's "outright europhobes" have been marginalised.

A stronger Europe would also act as a balance for America and Britain's historic ties with the US make it ideal to lobby on the EU's behalf, he said.

"The EU could do much more to promote peace and security. Washington is not the fount of all strategic wisdom. A stronger Europe would bring added value to any joint western strategy for security. Britain should use its ties with the United States to promote the European case."

He also stressed the importance of the Commonwealth, which should have a higher place on Britain's agenda.

"The Commonwealth is particularly important in the perspective which it gives us on the problems of some of the poorest countries in the world," he said.