(CNN) -- World leaders reacted with shock and condemnation Thursday to the assassination of former Pakistan Prime Minister Benazir Bhutto, some expressing concern about the nation's democratic process.
Benazir Bhutto died Thursday after a suicide bombing at a political rally in Rawalpindi, Pakistan.
The opposition leader died after a suicide bombing at a political rally in the Pakistani city of Rawalpindi ahead of parliamentary elections set for January 8.
President Bush, vacationing at his Texas ranch, condemned the assassination as a "cowardly act by murderous extremists." See Bhutto shortly before her death »
In Washington, the State Department also condemned the attack. "It shows people are still intent on undermining democracy in Pakistan," said deputy spokesman Tom Casey.
Pakistan -- which maintains nuclear weapons -- has been a key ally of the United States during its war against al Qaeda and Taliban terrorists in neighboring Afghanistan. Watch mourners crowd around Bhutto's casket »
Afghan President Hamid Karzai had met with Bhutto just hours before her death.
Karzai said Bhutto "sacrificed her life for the sake of Pakistan, and for the sake of this region." She had "love and desire for peace in Afghanistan, for prosperity in Afghanistan, and for Afghanistan and Pakistan that would be happy, prosperous and have good relations with each other," said the Afghan president.
"... we have lost one of our important, very important and, I would stress, liberal leaders," Durrani said.
For months, the Bush administration has been encouraging Pakistani President Pervez Musharraf to work out a compromise with his political opponents, including the popular Bhutto. The former prime minister's party is widely expected to do well in next month's elections. See timeline »
Bhutto's killing prompted Musharraf to declare three days of national mourning and to call on Pakistanis for solidarity and cooperation. "This is the work of those terrorists with whom we are engaged in war," said Musharraf. "I have been saying that the nation faces the greatest threats from these terrorists."
Saying he was "deeply shocked," British Foreign Secretary David Miliband called for restraint and unity in the aftermath of the assassination in the former British colony. Bhutto "knew the risks of her return to campaign but was convinced that her country needed her," Miliband said in a statement. Watch UK Prime Minister Gordon Brown: 'It's a sad day for democracy" »
French Foreign Minister Bernard Kouchner, who knew Bhutto personally, "expressed vivid emotion following the attack," said a statement from his office.
Kouchner strongly condemned "this horrible act" and "reaffirms France's commitment to the stability of Pakistan and its democracy," the statement said.
In India, which has long had a thorny relationship with its neighbors in Pakistan, an Indian Congress Party spokesman told the Press Trust of India, "... we must express our deep concern at anything that disrupts and disturbs the even keel of democratic governance in Pakistan."
The spokesman, Abhishek Singhvi, said Indian democracy loathes violence, saying "it is not only anti-democracy but also generates instability."
In Iran, Foreign Ministry spokesman Mohammad Ali Hosseini said in a statement, "We hope the Pakistani government will identify and bring to justice those behind such a criminal act and restore tranquility to the country."
Russia's Foreign Ministry called Bhutto's death a terror attack.
"We strongly condemn this terrorist act, present our condolences to the family and friends of Benazir Bhutto and hope that Pakistani authorities will provide for national stability," said Russian Foreign Ministry spokesman Mikhail Kamynin.
The Russian Foreign Ministry has repeatedly expressed concern that the Pakistani government "must do its best to ensure the maximum stability in the election period and prevent terrorist acts against Benazir Bhutto and other political leaders," said the Kamynin statement.
The rally bombing took place as Bhutto campaigned for a third term as prime minister.
It was the second recent attack on Bhutto after she defied death threats and returned to her homeland from eight years of self-imposed exile. On October 18, a suicide bomber targeted her motorcade in Karachi, killing 136 people. Bhutto was unhurt in the attack. E-mail to a friend