President Bush said last night the United States was determined to get terrorist mastermind Osama bin Laden "dead or alive".

Bin Laden is the prime suspect for overseeing last week's terrorist attacks on America and is in hiding under the protection of the Taliban regime in Afghanistan.

Mr Bush said: "I want justice. There is an old poster out west that says Wanted: Dead or Alive."

Today, Afghanistan is expected to decide whether to hand over bin Laden in a desperate attempt to stave off American military action.

As Britain signalled it was ready to join US strikes against Afghan-istan, Taliban supreme leader Mullah Mohammed Omar said a grand council of Islamic clerics would decide whether to comply with US demands.

The move, reported by Kabul radio following talks with a high-level delegation from neighbouring Pakistan, was the first sign that the Taliban may be cracking in the face of the intense international pressure.

It was expected that Pakistan, led by intelligence chief Lieutenant General Mahmood Ahmed, would meet the 20-strong grand council of Islamic clerics in the capital Kabul.

The Taliban has previously strongly resisted demands to hand over bin Laden, who is described as a "guest" of the regime.

Earlier, Foreign Secretary Jack Straw said British intelligence had independently established that bin Laden was the prime suspect for the attacks on the World Trade Centre and Pentagon.

The move cleared the way for UK forces to take part in military action after Prime Minister Tony Blair said at the weekend that Britain would be making its own judgment on who was responsible for the suicide attacks.

"That assessment underlies the judgements we will be making in the days and weeks ahead," Mr Straw told a news conference at the Foreign Office in London.

The threat was underlined by Mr Blair, who later told reporters in Downing Street: "In ordinary, everyday terms, we are at war with the people who have committed this terrible act."

Mr Bush, who was briefed yesterday on the possible military options, said that the US would take the "necessary actions" to defeat terrorism.

But he also warned Americans about the "sacrifice" they would have to make.

"Freedom has a cost and we are willing to bear that cost, " he said.

"An act of war has been committed against this country."

On a day of intense diplomatic activity, it was announced that an emergency summit of European Union leaders would be held in Brussels on Friday to discuss the crisis.

Mr Blair, who was involved in a continuous series of diplomatic contacts throughout the day, spoke by telephone for 15 minutes to Pakistan's President Pervaiz Musharraf.

As a key supporter of the Taliban, Pakistan is one of the few nations thought to be capable of influencing the hardline Islamic regime.

But with the expectations of US military action growing - possibly within the next few days - tension between Afghanistan and Pakistan appeared to be increasing.

Both sides were said to be massing troops along their border and there were even reports that the Taliban had deployed Scud missiles.

Pakistan sealed its side of the frontier, preventing hundreds of thousands of Afghans fleeing possible US air strikes from entering the country.

Despite expressing "full and tangible" support for America, Mr Straw urged the US administration to exercise caution in choosing what course of action to pursue.

He said the current situation was the "most worrying" to face the world since the Cuban missile crisis of the 1960s brought the US and the Soviet Union to the brink of nuclear war.

"We are determined that decisions are made in a cool, measured and intelligent way," he said.

* The Prime Minister hopes to visit the scene of devastation in New York on a visit to the US later this week.

Mr Blair is to fly to Washington for talks with President Bush on Thursday before possibly going to New York to see the carnage inflicted by the terrorists.

He wants to visit New York to show support for the emergency services and to meet relatives of British victims, said a No 10 spokeswoman.