Speaking on BBC One's Breakfast with Frost Mr Hoon said the UK reserved the right to use the weapons "in extreme self defence".

Saddam can be absolutely confident that in the right conditions we would be willing to use nuclear weapons                                 Geoff Hoon Defence Secretary

It is widely reported that before the first Gulf War the US and its allies made it
known to the Iraqi leader that nuclear weapons would be the response to any use of chemical or biological weapons.

On Friday Mr Hoon's Cabinet colleague, International Development Secretary Clare Short, said she could foresee no scenario in which a retaliatory nuclear strike would serve any useful purpose.

Mr Hoon contradicted her view, saying nuclear weapons could not be a deterrent if
there was no willingness to use them.

Confident on resolution

He said: "We have always made it clear that we would reserve the right to use nuclear weapons in conditions of extreme self defence."

"Saddam can be absolutely confident that in the right conditions we would be willing to use nuclear weapons."

Action could be in 'weeks not months'

Mr Hoon said there was no fixed timetable for war.

A further discussion was necessary in the United Nations Security Council after a material breach of resolution 1441 was declared.

He said that if and when that happened, the UK would make "a very determined effort" to secure a second UN resolution giving backing for military action against the Iraqi leader.

"We are confident there will be a second resolution," added Mr Hoon.

Inspectors toughen

Saddam had been give a "last chance" with the original resolution, but he was
failing to cooperate with the inspectors and "the clock is ticking".

Mr Hoon, who said he would welcome any sign of Saddam cooperating with the weapons inspectors, added that a statement on a RAF deployment to the Gulf would be made to the House of Commons soon.

Mr Mbeki held talks with Blair

Meanwhile the United Nations chief weapons inspectors have set tough new conditions for holding a fresh round of talks with Iraqi officials.

UN officials said Hans Blix and Mohamed ElBaradei will return to Baghdad on 8 February, but are insisting on greater co-operation from Iraq on issues including surveillance flights and interviews with scientists.

US President George W Bush has warned he will not tolerate any attempt by Baghdad to delay possible military action by "stringing along" inspectors.

Arms experts were stymied again on Saturday when a 17th Iraqi researcher
refused to meet them alone.

Alliance building

As the progress towards apparent war continues, US Secretary of State Colin Powell is expected to unveil a US dossier on Iraq's weapons of mass destruction to the UN on Wednesday.

The alliance building continues, with UK Prime Minister Tony Blair and South African President Thabo Mbeki meeting on Saturday for talks on issues including Iraq, the Middle East peace process, African development and Zimbabwe.

The unpredictable diplomatic game goes on

Click here for analysis on Blair's trip

Although Downing Street described them as "cordial", President Mbeki told Sky News' Sunday with Adam Boulton that South Africa was concerned about military action against Iraq.

The previous day Mr Blair and President George W Bush stood united in their pledge to disarm President Saddam Hussein "in a matter of weeks not months" at their White House summit.

Next week Mr Blair will meet French President Jacques Chirac, who appears reluctant to back the US position on Iraq.

Mr Blair told BBC Radio 4's Today programme on Saturday he did not believe Mr Bush would disregard the UN.

Nelson Mandela

He added that "even now" Saddam Hussein could avoid war by co-operating fully with the weapons inspectors.

Tony Blair is... the foreign minister of the United States                                 Nelson Mandela Ex-South African President

But he said: "It is really a question of whether people believe Saddam is likely to comply or not.

"Personally I think it is frankly obvious he is not."

The South African leader's predecessor, Nelson Mandela has accused the prime minister of arrogance and short-sightedness.

He said Mr Blair was "no longer prime minister of Britain" but instead "the foreign minister of the United States".