The government must provide more clarity over its stance on Iraq, Charles Kennedy has said.

The Liberal Democrat leader also confirmed that he would be prepared to take part in next weekend's "stop the war" rally in central London.

Kennedy said his message to protestors would be that military action might prove necessary if it is conducted with the full authority of the United Nations.

Meanwhile, chancellor Gordon Brown has pledged that he will find whatever money is needed to fund continuing operations in the Middle East.

But speaking on Sunday, Kennedy called on the government to explain what would happen after the initial fighting was over.

"Once we prosecute such a war, what are we going to do about the peace? Who are we going to put in power? Who is going to police it? What is going to be the role of the British forces?

"We have not had adequate answers to this question," he said.

Speaking on BBC One's Breakfast with Frost programme, the Lib Dem leader said military leaders also needed clear instructions from the government.

"I don't think that the British House of Commons or the British government is fulfilling its purpose properly unless it issues clear guidelines with objectives.

"I don't think that is fair on the military personnel who, as we speak, are being deployed and will be risking their lives," he said.

Kennedy also indicated there was a contradiction between the prime minister's statements in support of both the United Nations and president Bush.

"He seems to be saying that we can as a country, at one and the same time, pursue the United Nations line...but at the same time you have president Bush saying the game is essentially up, time is gone, we have made the call and that Britain will regardless go along with the American administration.

"Those are not consistent arguments. They are inconsistent with each other and I think we need more clarity from the prime minister. I think that is what the country wants."

But the prime minister's position was backed by Gordon Brown.

He told the BBC that Tony Blair was "absolutely right" to take a tough line against Saddam Hussein.

"I believe that the British people will come to the view that this is the right course of action, that we must stand up to dictators who defy the international community by having weapons of destruction and failing to disclose them and even trying to find the means of deceiving people about the disclosure," he said.

And following estimates that a war could cost Britain £3.5 billion, with peace keeping operations increasing the bill further, Gordon Brown also predicted that financial support could be made available by the international community.

"I believe that people will want to share the costs, if there is and there has to be action, and there is this aftermath that people talk about.

"I think the international community will want to share the costs of that, as has happened in Afghanistan as has happened in Kosovo," he said.