The United States is stepping up security at "soft targets" like hotels and shopping malls, as well as trains and ports, as it counters the evolving al Qaeda threat, a top official said Sunday.
A year after a foiled plot to bomb a US-bound passenger plane, Homeland Security Secretary Janet Napolitano told CNN's "State of the Union" program that other places and modes of transportation must now be scrutinised.
"We look at so-called soft targets - the hotels, shopping malls, for example - all of which we have reached out to in the past year and have done a fair amount of training for their own employees," Napolitano said.
Since an attempted bombing on a packed Saturday night in Times Square in May, New York, for example, has installed hundreds of security cameras as part of a plan to triple the number of cameras to 3,000.
In September, the city activated some 500 new surveillance cameras at its three busiest subway stations - Times Square, Penn Station and Grand Central.
"The overall message is everything is objectively better than it was a year ago, particularly in the aviation environment. But we're also looking at addressing other areas," Napolitano said.
As extremists struggle to circumvent tighter security at airports and search for new avenues, she said US officials were looking to step up broader measures.
"What we have to do is say, well, what other ways are they thinking to commit an act, because our job is not only to react, but to be thinking always ahead, what could be happening," Napolitano said.
"And so we have enhanced measures going on at surface transportation, not because we have a specific or credible threat there, but because we know, looking at Madrid and London, that's been another source of targets for terrorists."
Suicide bombers killed 52 people aboard a bus and three London Underground trains in 2005.
And in Europe's worst terror attack, 191 people were killed and nearly 2000 injured in Madrid in March 2004 when 10 backpacks filled with nails and explosives went off on four trains during morning rush hour.
"It means, as we make the land borders harder to cross from a land border crossing standpoint, that we need to be looking out into our coasts and to the waters," said Napolitano.
Last Christmas, Umar Farouk Abdulmutallab, a young Nigerian who claims to have been trained by al Qaeda operatives in the Yemen, failed to detonate explosives concealed in his underwear on a packed transatlantic airliner as it came in to land in Detroit.
The US authorities responded by installing new screening machines and initiating draconian body searches at airports.
Napolitano said international travellers in the United States also face tight intelligence screening even before they reach the boarding gate.