President Bush joined his Pakistani counterpart, Gen Pervez Musharraf, in condemning a grenade attack on a Protestant church in Islamabad yesterday that killed five people, including two Americans.
Mr Bush, who has relied on Gen Musharraf as a key ally in the US-led war on terror in Afghanistan, said he was "outraged by the terrorist attack" which also wounded 42 people, and vowed to work closely with Pakistan to find those responsible.
"I strongly condemn them as acts of murder that cannot be tolerated by any person of conscience nor justified by any cause," Mr Bush said in a statement issued by the White House.
There was no claim of responsibility for the attack in Islamabad's diplomatic enclave but suspicion fell on hardline Islamic groups opposed to Gen Musharraf's support for Washington's anti-terror campaign.
Gen Musharraf - who has banned several militant groups and ordered the arrest of hundreds of militants since the September 11th attacks on the US - called the assault a "ghastly act of terrorism", state media reported.
Witnesses and the government said a lone attacker entered the church during the sermon and threw about six grenades, killing two Americans, one Pakistani, one Afghan and another person whose body was blown to pieces by the blasts.
The two Americans have been identified as Ms Barbara Green, the wife of a US diplomat, Mr Milton Green, and their teenage daughter Kristen.
"The nefarious act is aimed at sabotaging the interests of Pakistan at a time when the country is actively engaged in eliminating terrorism," Gen Musharraf said.
Gen Musharraf, who seized power in a bloodless 1999 coup, had ordered security agencies to launch "a co-ordinated hunt to track down the culprits involved in the dastardly attack", the state news agency APP said.
But the head of Pakistan's main Islamic party called the attack a failure by the military government and its security agencies to protect lives and property.
"There is no ground to blame any internal religious group for this," the Jamaat-e-Islami leader, Mr Qazi Hussain Ahmed, said. "We condemn this act in the strongest words and assure the Christian minority that we fully share their grief and tragedy and will support any action against people who did this."
In London, the British Foreign Secretary, Mr Jack Straw, said he was "deeply shocked". He added: "I want to express my condolences on behalf of Her Majesty's government to the families of those who have been killed and to all those who have been injured."
The US ambassador to Pakistan, Ms Wendy Chamberlin, went to the Federal Government Services Hospital where she viewed the bodies and visited the wounded. She emerged after about an hour looking grim, saying: "It's a tragedy". Asked what the motive could be, she said simply: "Terrorism."
Later she described the Americans victims as "members of the embassy family . . . two friends I admired, respected and I loved.
"I honour them for their lives, for the joy they brought to so many and for the credit and honour they brought to the United States," she said.