Some travellers argue increasingly invasive airport security infringes on their civil rights [GALLO/GETTY]

The US government's department for Homeland Security is alerting air carriers to a potential new bombing tactic involving insulated beverage containers like thermoses, according to an official.

The official, who spoke on condition of anonymity, stressed on Friday that there is no intelligence about an active "terror plot".

However, he said travellers may notice that airport screeners are taking a closer look at empty insulated containers, although authorities have no information about a specific threat involving the items.

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The department regularly alerts law enforcement about evolving "terrorism" tactics, as counterterrorism officials learn about them through intelligence channels.

The warning comes as President Barack Obama's government seeks to reassure the US public of its handling of domestic security, after what has been a challenging year.

Following a failed attack last Christmas Day on a US-bound airliner, the administration has faced an attempted car bombing in Times Square, a nearly successful attack on US-bound cargo planes and several nascent plots disrupted by the US Federal Bureau of Investigation (FBI).

Increasingly invasive airport security has drawn criticism from some travellers, who argue it infringes on their civil rights.

'Potential bad news'

Eric Holder, the country's attorney-general, told ABC television earlier this week that he is most worried about attacks on the US by Americans. High on his list of concerns is the threat posed by the anti-American cleric Anwar al-Awlaki, a US citizen believed to be hiding in Yemen.

Holder said in the interview that the so-called terrorism threat is real and constant, and that he's concerned that authorities may have missed a signal that an attack is imminent.

He said Americans have to be prepared for "potentially bad news".

However, John Brennan, the White House's senior counterterrorism advisor, said on Wednesday that the mistakes that had allowed a bomber to board a plane last Christmas have been fixed.

"We are in a much better position today than we were last year at this time," Brennan said.

Source: Agencies