"We stand with the people of Pakistan in their struggle against the forces of terror and extremism," the President said in a statement.
'The United States strongly condemns this cowardly act by murderous extremists who are trying to undermine Pakistan's democracy. Those who committed this crime must be brought to justice. Mrs Bhutto served her nation twice as prime minister and she knew that her return to Pakistan earlier this year put her life at risk. Yet she refused to allow assassins to dictate the course of her country,' Bush said.
He also conveyed his sympathy on the occasion, saying "Laura and I extend our deepest condolences to the family of Benazir Bhutto, to her friends, to her supporters. We send our condolences to the families of the others who were killed in today's violence. And we send our condolences to all the people of Pakistan on this tragic occasion.'
Secretary of State Condoleezza Rice said that Bhutto's passing is a great loss for Pakistan. 'I knew her as a woman of great courage and had been impressed by her dedication and commitment to democracy and to the future of Pakistan itself.'
'The deadly results of this attack will no doubt test the will and patience of the people of Pakistan. We urge the Pakistani people, political leaders, and civil society to maintain calm and to work together to build a more moderate, peaceful, and democratic future,' Rice said.
United Nations Secretary-General Ban Ki-moon said the attack 'represents an assault on stability in Pakistan and its democratic process. While strongly urging calm and restraint to be maintained at this difficult time, I call on all Pakistanis to work together for peace and national unity,' he added.
An emergency meeting of the UN Security Council also condemned the terrorist attack and called on all Pakistanis to show restraint and ensure stability in the country.
In a statement, New York City Mayor Mike Bloomberg said, 'Today all New Yorkers, including the more than 1,00,000 who can trace their heritage to Pakistan, are saddened to learn about the assassination. Hers was a voice for democracy, and the silencing of it by such brutal means is a shock to us all. The perpetrators of this violent act must be brought to justice, and it is my hope that President Musharraf will follow through on free and fair elections in January as a testament to Bhutto's legacy.'
Experts said that the assassination could have profound effects on the future of Pakistan and, to a lesser extent, on the rest of South Asia.
'This is a devastating blow to the cause of democracy in Pakistan," said Teresita Schaffer, director of the South Asia Program at the Center for Strategic and International Studies and an old South Asia hand.
'It leaves everyone worse off: the PPP has lost a leader; Nawaz Sharif too was attacked the same day; Musharraf looks either complicit or incompetent, and there's a significant chance that the elections won't take place in the manner he had planned. I don't know who was responsible but inevitably some people will believe ISI was involved, so the army's prestige is likely to fall further," observed Teresita, adding "For the US, [there are] two big issues: what happens next in Pakistan, where there has been a lot of unrest (and that will continue); and, will the Pakistan government be able to pay any attention to the frontier areas. My guess is, not for the time being. This is bad news for the US.'
P J Crowley, a senior fellow at the Washington, DC-based Center for American Progress thinks that the murder could lead to another Emergency.
'This was an attack on the remnants of democratic and civil society in Pakistan. How Pakistan responds to this will say a lot about its future. Musharraf declared martial law less to deal with growing unrest but to assure himself another term in office. Now there will be great pressure placed on Musharraf to deal with extremists. There will be questions about the involvement of intelligence and security services in these movements. Musharraf may be forced to re-impose emergency rule, which will push back the very democratic reforms that are important to Pakistan's future and stability,' he said.
"I last met with Benazir Bhutto on September 26 when she came to my office just days before returning to Pakistan. She was aware of her personal danger. She expressed a strong appreciation for President Musharraf's challenges in running the country, and she was hopeful that her return would be a force toward securing a national election and advancing democracy in Pakistan," US Senate Foreign Relations Committee Ranking Member Dick Lugar said.
"I reiterate President Bush's call for continuing with the election on January 8 in honour of Benazir Bhutto's memory," he said.
Congressman Joseph Crowley (D-NY), a member of the House Committee on Foreign Affairs, said that the government and the people of Pakistan must use Bhutto's legacy to create a true democracy in Pakistan.
"Pakistan is on the front line in the world's war against terror. Bhutto's death should open all of our eyes to the threat that still exists in Pakistan and the surrounding region, and it must inspire the global community to renew its efforts to combat terrorism," he said.
"Bhutto was a stalwart of moderation, a force for democratic values, and a personal friend," said Congressman Tom Lantos, chairman of the House Foreign Affairs Committee, adding,
"We urge them to honour Benazir Bhutto's memory by continuing with the democratic process for which she so bravely gave her life," Bush told reporters before calling up Musharraf.