The United States raised its terrorist threat level to "high" last night, indicating the possibility of attacks which Tom Ridge, the director of Homeland Security, said could "rival or exceed what we experienced on 11 September".
Mr Ridge said there had been an increase in the volume of intelligence reports and he cited renewed concerns about the use of aircraft as weapons. "We continue to hear ... the interest in using aircraft as a means of attack," he said. In the colour-coded scheme that his department devised, the threat went from yellow to orange, the second highest level.
The alert has an impact on law enforcement agencies, including those who carry out security checks at airports.
But Mr Ridge said Americans should not alter their holiday travel plans. He said the increased "chatter" picked up by intelligence agencies had "no connection" with the capture of Saddam Hussein on 13 December. He said he had heard about a report that a female suicide bomber might be planning an attack in New York, but said that he had "no independent confirmation" to corroborate the story.
In Britain, Tony Blair is planning to capitalise on Libya's agreement on Friday to surrender its weapons of mass destruction by trying to persuade Iran and Syria to follow suit. British officials are to step up efforts in the new year to argue that the nations should give up plans to develop illicit weapons in return for closer links with the West.
Relations have warmed recently with Iran, which agreed last week to allow United Nations inspectors access to potential nuclear sites. Britain has said that it believed the Tehran regime would co-operate, but stressed that Iran would be judged on its actions rather than its words. There were also concerns that Iran might still possess chemical and biological weapons.
Syria, which has been accused by the United States of supplying Saddam with arms, has failed to sign up to international agreements on chemical and biological materials.
The Foreign Office said Syria was "another country of interest to us" and the Government was pressing it to ban such materials as soon as possible.
Libya agreed yesterday to allow snap UN nuclear arms inspections. The Prime Minister, Shokri Ghanem, said economic progress was more important than arms. He said: "We are turning our swords into ploughshares and this step should be appreciated and followed by all other countries."
But Britain said that the situation in Iraq might have prompted the move. Geoff Hoon, the Defence Secretary, said: "We showed after Saddam Hussein failed to cooperate with the United Nations that we meant business and Libya, and I hope other countries, will draw that lesson."
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