The UK is to set up a global database of extremists who face automatic vetting before being allowed in, Home Secretary Charles Clarke has told MPs.
Tony Blair: International conference
He said the database would list "unacceptable behaviour" such as radical preaching, websites and writing articles intended to foment terrorism.
Individuals' presence on the list means they may face exclusion from the UK.
Hopes for an international conference on Islamic extremism were also outlined by Prime Minister Tony Blair.
Mr Clarke told MPs he wanted to apply more widely the home secretary's powers to exclude an individual from the UK if their presence is deemed "not conducive to the public interest".
In a Commons statement he said: "In the circumstances we now face, I have decided that it is right to broaden the use of these powers to deal with those who foment terrorism or seek to provoke others to terrorist acts.
"I intend to draw up a list of unacceptable behaviours which would fall into this - for example preaching, running websites or writing articles which are intended to foment or provoke terrorism."
He said there would be consultation before the final list of "unacceptable behaviours" was decided upon.
Mr Clarke said he had asked the Home Office, Foreign Office and the intelligence agencies to "establish a full database of individuals around the world who have demonstrated relevant behaviours".
Anyone wanting to enter the UK would then be checked against this list - and if they are on it they may be refused permission to enter the country.
In a statement on the aftermath of the London bombings in which 56 people died, Mr Clarke also said he planned a new offence of "indirect incitement to terrorism", to add to the current offence of direct incitement.
He said it "targets those who, while not directly inciting, glorify and condone terrorist acts knowing full well that the effect on their listeners will be to encourage them to turn to terrorism".
Earlier, at prime minister's questions, Mr Blair told MPs the UK was looking at holding an international conference for countries concerned about or affected by Islamic extremism.
He said the aim was "to try and take concerted action across the world to try to root out this type of extremist teaching".
He said: "Though the terrorists will use all sorts of issues to justify what they do, the roots of it do go deep, they are often not found in this country alone therefore international action is also necessary."
Mr Clarke, during his statement, said the UK had reached an agreement with Jordan which would enable Britain to deport Jordanian nationals suspected of inciting or supporting terrorism.
Under international convention the UK government cannot send people back to a country where they might face mistreatment or the death penalty.
Abu Qatada could face deportation
The memorandum of understanding removes this bar to deportations.
However, Amnesty International's UK Director Kate Allen said promises from countries like Jordan, known to have used torture, "are not worth the paper they are written on".
She questioned how Mr Clarke would monitor whether these promises were being kept.
Jordanian-born cleric Abu Qatada could face deportation as a result of the agreement.
Court challenges mean it is likely to be months before deportations happen.
Convicted in absence
The government is seeking similar "memorandums of understanding" with a number of North African countries.
The prime minister's official spokesman said there were a number of Jordanian nationals who may be subject to deportation proceedings after the memorandum is signed, but he refused to disclose any further details.
Abu Qatada, who fled to the UK claiming persecution and was held in Belmarsh Prison without charge as part of the government's post-11 September crackdown, is currently subject to a control order.
Police uncovered tapes of his sermons at a Hamburg flat used by some of the 11 September hijackers.
He has been convicted of terrorism in his absence in Jordan and several European countries are believed to be trying to extradite him.