WASHINGTON, Jan 9: The US government on Friday lowered the national terror threat level to "elevated" from "high", though security will remain tight in some sectors, including aviation.

Homeland Security Secretary Tom Ridge announced the reduction in the colour-coded threat level to "yellow" from "orange", but said airlines, other sectors and some unspecified parts of the country would be asked to remain on a heightened state of alert to guard against possible terror attacks.

"We are still concerned about continued threats, but the threat condition we have been following has diminished," he said at a news conference. "With the passing of the holidays and many large gatherings ... we have made the decision to come down to yellow."

The alert level was raised to "orange" - the second highest threat level - on Dec 21. At the time Mr Ridge warned of a high risk of an attack around the Christmas and New Year holidays that could be bigger than those of Sept 11, 2001.

Since then, US authorities have passed on intelligence regarding specific threats to airlines, prompting carriers in Britain, France and Mexico to cancel several flights.

The United States also ordered foreign airlines to put armed marshals on some flights and dispatched fighter jets to escort some incoming planes. The five-level colour-coded scheme, established to help Americans better prepare for future attacks, has generally held steady at "yellow" but has been raised to "orange" five times since it was created in March 2002.

Ridge said the heightened alert helped over the busy holiday season. "The potential danger that large gatherings present during the holidays has passed," he said. "They passed safely and without incident."

Though Mr Ridge would not specify the sectors the government is most concerned about, he said intelligence shows airlines are still at risk. "One of the most persistent and consistent reports we have from multiple sources (is) the continued interest by al Qaeda ...to use aircraft, but particularly commercial aircraft," he said.-Reuters