LONDON — Britain raised its terror threat alert to the second-highest level Friday, one of several recent moves the country has made to increase vigilance against international terrorists after a Christmas Day bombing attempt on a Europe to U.S. flight.
The threat level was raised from "substantial" — where it had been since July to indicate a strong possibility of a terrorist attack — to "severe," meaning such an attack is considered highly likely.
In making the announcement, Home Secretary Alan Johnson said raising security level means that Britain is heightening its vigilance. But he stressed that there was no intelligence suggesting an attack is imminent.
"The highest security alert is 'critical,' and that means an attack is imminent, and we are not at that level," he said on British television.
Johnson declined to say what intelligence the change was based on or whether the move was related to the failed Christmas bombing attempt, when U.S. authorities say a young Nigerian named Umar Farouk Abdulmutallab tried to detonate a bomb hidden in his underwear during a flight from Amsterdam to Detroit. Abdulmutallab, who allegedly had links to extremists based in Yemen, had studied as a university student in London.
Friday's change came days after Britain suspended direct flights to Yemen's capital in response to the growing threat from al-Qaida-affiliated militants based in that country. Prime Minister Gordon Brown said his government also was creating a new terrorist no-fly list and targeting specific airline passengers for tougher security checks.
The measures followed a discussion between Brown and President Barack Obama on Tuesday. They match similar moves made by U.S. authorities last week to enhance security at airports and on planes, as intelligence officials warned that al-Qaida's branch in Yemen was continuing to plot attacks on the United States.
Britain's five-tiered alert system — which starts at "low" and passes through "moderate," "substantial," and "severe" before hitting "critical" — is similar to the U.S. system of color-coded terrorism advisories.