PAKISTAN was on a knife-edge last night after the assassination of Benazir Bhutto.

The country's former prime minister was shot by a suicide bomber who then blew himself up moments after she addressed thousands of supporters in the city of Rawalpindi.

The killing came less than two weeks before elections many expected to return her to power and restore the nuclear armed nation to the democratic fold.

There were immediate predictions of civil war in the strife-riven country -a linchpin of George Bush's war on terror -despite international calls for restraint and unity.

The murder was condemned across the world, including by Prime Minister Gordon Brown, who said she had been "assassinated by cowards afraid of democracy".

US President Bush said Ms Bhutto "gave her life" for the democratic process.

He said that by returning to contest the elections despite the threat to her safety, she "refused to allow assassins to dictate the course of her country".

Descriptions of Ms Bhutto as a martyr by supporters of her Pakistan People's Party were echoed by Hamid Karzai, president of neighbouring Afghanistan, who met her only hours before her murder.

Although the attack was said to carry the hallmarks of Taliban-inspired Islamic extremists, much of the fury was directed against Pakistan president Pervez Musharraf, who was accused of failing to protect her.

Outside the hospital where Ms Bhutto died, some even chanted: "Killer, killer, Musharraf, killer."

Supporters held angry protests in several cities, attacking police, smashing vehicles and starting fires.

Ms Bhutto's long-term political rival, fellow former prime minister Nawaz Sharif, paid his respects in person to her body last night before he emerged to describe her as a sister and pledged to "take the revenge on the rulers".

Announcing three days of mourning, Mr Musharraf appealed for calm and insisted that the killing was the work of terrorists.

But doubts now hang over whether elections scheduled for January 8 will take place.

Mr Sharif said his party would boycott the elections and called on Mr Musharraf to stand down immediately.

While many called for the vote to be postponed, President Bush urged the people of Pakistan to honour Ms Bhutto's memory by continuing with the democratic process.

The crisis was felt beyond the borders of Pakistan, and the UN Security Council met last night for closed discussions.

Criticised as too pro-Western by her enemies, Ms Bhutto had become a vocal critic of the influence of the Taliban both across the border in Afghanistan, where more than 7,000 British troops are deployed, and in Pakistan.

Mr Karzai described Ms Bhutto as "the daughter of Pakistan and of the Muslim world".

He said: "I found her to be a very, very brave woman with a clear vision for her own country, for Afghanistan and for the region. We in Afghanistan condemn this act of cowardice and immense brutality.

"She sacrificed her life for the sake of Pakistan and for the sake of this region."

After years of self-imposed exile, much of it in London, Ms Bhutto returned to her homeland in October to contest the elections, only to face an immediate assassination attempt.

Critics said she was naive to continue campaigning despite the security risks, but supporters praised her as brave.

Despite a previous suicide attack on her motorcade, her assassin was able to strike as she waved to a thronging crowd from the roof of her armoured vehicle.

But Mr Bush said: "She refused to allow assassins to dictate the course of her country"

Gordon Brown said: "Benazir Bhutto was a woman of immense personal courage and bravery.

"She risked everything in her attempt to win democracy in Pakistan.

"She has been assassinated by cowards afraid of democracy. Benazir Bhutto may have been killed by terrorists, but the terrorists must not be allowed to kill democracy in Pakistan."