Prime Minister Gordon Brown today condemned the Jerusalem massacre, describing it as "an attempt to strike a blow at the very heart of the peace process".
He spoke out after a gunman fired hundreds of rounds in an attack on a religious seminary, killing at least eight.
Mr Brown, speaking in No. 10, said: "Last night's attack and the murders that took place in Jerusalem will mean that the whole world will be outraged at what has been happening.
"This is clearly an attempt to strike a blow at the very heart of the peace process."
Mr Brown said he had sent his condolences to Israeli Prime Minster Ehud Olmert.
A man armed with an assault rifle and a pistol yesterday opened fire in the library of the Mercaz Harav rabbinical college, where around 80 students had gathered for a party.
Nine people are thought to have been wounded in the attack, two seriously, according to Israeli officials.
US president George Bush joined in condemnation of the killings.
"I condemn in the strongest possible terms the terrorist attack in Jerusalem that targeted innocent students," he said.
Foreign Secretary David Miliband last night said he had spoken to his Israeli counterpart and passed on his condolences.
"The reports of killings at a seminary in Jerusalem are shocking," he said.
"They are an arrow aimed at the heart of the peace process so recently revived. They should and will be deplored by all decent people everywhere."
The incident is the first militant attack in the Israeli capital in more than four years, and though no-one has claimed responsibility, Hamas militants in the Gaza Strip praised the operation, while thousands of Palestinians took to the streets of Gaza to celebrate.
No words could comfort the bereaved families, Mr Miliband said.
"The only way to honour the memory of those who have died is to build a Middle East free from the power of the gun through a political process in which the peaceful majority drive out the murderous minority," he said.
Conservative leader David Cameron said: "I utterly condemn the appalling terrorist attack that has taken place in Jerusalem. I send my profound condolences to the families and friends of all of those who have been killed, and to those who have been injured."
David Simchon, the head of the seminary, said the students had been preparing for a party for the festival of Purim and instead found themselves involved in a massacre.
Yehuda Meshi Zahav, the head of the Zaka rescue service, said: "The whole building looked like a slaughterhouse. The floor was covered in blood.
"The floors are littered with holy books covered in blood."
The attacker was apparently shot by a student before being killed by an Israeli soldier.
Palestinian president Mahmoud Abbas condemned the killings, which came on the same day as Egyptian officials were trying to mediate a truce between Palestinian militants and Israel.
"The president condemns all attacks that target civilians, whether they are Palestinian or Israeli," he said.
But the Israeli government said condemnation was not enough.
"The massacre in Jerusalem is a defining moment," spokesman Mark Regev said.
"It is clear that those people celebrating this bloodshed have shown themselves to be not only the enemies of Israel but of all of humanity.
"The government of the Palestinian Authority has an obligation not just to condemn this brutal act of violence in Jerusalem but to take substantial steps against terror infrastructure."
President of the Board of Deputies of British Jews Henry Grunwald said: "I utterly condemn this cowardly act of terror at the Mercaz Harav Yeshiva in Jerusalem.
"The deliberate mass murder of innocent teenagers in their place of study and prayer carries a particular revulsion, and is clearly designed to escalate an already tense situation.
"Whoever was responsible has no interest in peace, and Hamas' description of this murderous act as 'heroic' is an indication of their true intentions. Our thoughts and prayers are with the victims and their families."
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