Parliament will be recalled this Friday in the wake of the terrorist attacks in the US, the Prime Minister said today.
Mr Blair will make a statement to Parliament and Foreign Secretary Jack Straw will open a full debate.
Mr Blair said the security arrangements put in place yesterday will continue at least for the rest of the day as a "precautionary measure".
Most City businesses were functioning normally, he told a Downing Street news conference.
There will be a further meeting of the Cabinet's emergency committee today and the Prime Minister will chair a special Cabinet meeting tomorrow.
Mr Blair told the news conference he feared "significant numbers" of the casualties in the attacks would be British.
Such acts of terrorism required "a fanaticism and wickedness that is beyond our normal contemplation".
The Prime Minister, speaking in No 10's state dining room, added he was pleased to see statements of condemnation from British and American Muslim leaders, saying: "The vast majority of Muslims are decent, upright people who share our horror at what has happened."
He said the common cause of all democracies was now to "identify this machinery of terror and to dismantle it as swiftly as possible".
Mr Blair said that he had spoken to the leaders of Russia, France and Italy.
"We all agreed that this is an attack not only on America but on the free and democratic world," he said.
Speaking after a meeting this morning of the Cabinet's civil contingencies committee, Mr Blair told reporters: "We have agreed to keep in place the additional security measures that I announced yesterday, at least for the rest of the day.
"This is a purely precautionary measure but wise in the circumstances and I hope those who are suffering the disruption understand why we believe this to be necessary."
The premier said most financial institutions and businesses throughout the country were "functioning as normal".
The committee had also discussed what practical help Britain could offer America in dealing with the aftermath of the tragedy - but he gave no details.
Announcing the decision to recall Parliament on Friday, Mr Blair said he would make a Commons statement with Foreign Secretary Jack Straw then opening a full debate.
"I believe Parliament should be recalled both because of the sheer magnitude of the event, and its implications, but also because this was an attack not just on a number of buildings, but on the very notion of democracy.
"It is therefore all the more important that democratic voices are heard and in our country, Parliament is the place for that to happen."Reuse content