Britain, US lower terror threat level

But the authorities here warned that the threat of an attack had not disappeared and admitted that there would be confusion at airports as officials there grappled with the new security measures.

The British government early Monday downgraded the alert level to "severe," the fourth highest of five levels, from an unprecedented "critical," where it had stood since it announced Thursday it had foiled a major plot.

Following the British decision, the US Department of Homeland Security announced it was downgrading the threat level for inbound flights from Britain to "code orange" from "code red," its highest security risk alert.

On Thursday, British authorities arrested two dozen men suspected of plotting to smuggle volatile chemicals on to several passenger jets headed for the United States with the intent to set off explosions in mid-flight.

Britain's Home Secretary John Reid said that the threat of attack was no longer imminent as police "believe that the main suspects in the alleged plot were arrested last week."

But he warned that an attack remained "highly likely" as police investigated other suspected plots.

Transport Secretary Douglas Alexander said the new security picture meant that passengers would now be able to take aboard one item of hand luggage, though a ban on non-essential liquids and gels would remain in place.