Mr Clegg said he would not "condemn" UK forces to failure

The Liberal Democrats could stop supporting the UK's military presence in Afghanistan unless strategy is changed, leader Nick Clegg said.

He told BBC One's Politics show he wanted the mission to succeed but the present course was "almost certainly condemned to failure"".

Mr Clegg also said his party's backing for the war was not "unconditional".

The comments come after Prime Minister Gordon Brown pledged to send another 500 troops to Afghanistan.

There are currently about 9,000 UK military personnel in the country, while some 221 have been killed there since 2001.

'Heads held high'

The US government is debating a request for 40,000 more troops in Afghanistan.

Mr Clegg said: "Clearly no support that any political party gives for a conflict, for a war, is unconditional."

He also said: "The present strategy is failing so it needs to be changed and the discussions which are taking place in Washington at the moment are immensely important in working out whether we have got a strategy which will succeed.

"If that strategy, if that new strategy is, in our judgement, the wrong strategy, which will condemn our soldiers to failure, then of course we will revisit our support, of course."

He told Politics Show: "I think if we carry on, on the present course, we are almost certainly condemned to failure. I want us to succeed in Afghanistan."

"I want - when our servicemen and servicewoman leave Afghanistan - I want them to leave with their heads held high, feeling they've done a good job, a successful job, done what we're asking them to do not with a tail between their legs."

The SNP said Alex Salmond had the right to be included as a party leader

The SNP may take legal action if Alex Salmond is not allowed to take part in a UK party leader TV debate ahead of the next General Election.

The BBC, ITV and BSkyB jointly proposed three live debates between the Labour, Tory and Liberal Democrat leaders.

SNP Finance Secretary John Swinney said going to court was not being ruled out, but said it was more preferable to come to an agreement with the broadcasters.

Opposition parties accused the SNP of bullying tactics.

Tory leader David Cameron and Liberal Democrat leader Nick Clegg have welcomed a TV debate, while Gordon Brown has now said he was willing "in principle" to take part.

Mr Cameron has told the BBC he wants a respected independent figure to oversee the negotiations for the TV debates.

'Depriving voters'

But the SNP has threatened to seek to block the screening in Scotland of any debate which did not include Scottish First Minister Mr Salmond.

Mr Swinney told BBC Scotland's Politics show the SNP was the party of government at Holyrood, adding that the UK debates would discuss issues of importance to Scotland, such as the future of nuclear submarines on the Clyde.

Mr Swinney said the SNP was prepared to be flexible, saying of the current arrangements: "It deprives the voters in Scotland of hearing the breadth of political choice that quite clearly exists here in Scotland about the input of Scotland into the UK General Election."

Current plans would see the three main UK party leaders take part

On the issue of legal action, he added: "That might be a possibility, but, long before we get to that judgement, we have to have full and open discussions with the broadcasters about the arrangements that can be put in place."

Also speaking on the programme, shadow Scottish secretary David Mundell said it was not appropriate for Mr Salmond to take part in a debate about who should be the prime minister of Britain.

Labour described the SNP's option of going to court as a "sinister threat", and claimed, along with the Liberal Democrats, the Nationalists were attempting to bully broadcasters.

The broadcasters have said they would each seek "to make suitable arrangements for ensuring due impartiality across the UK", but have not yet explained how that would be achieved.