The US is taking additional air security measures in the wake of last month's airliner¹ bomb plot, a senior official has said.

美国一位高级官员称，针对上个月的飞机爆炸阴谋，美国正在采取附加航空安全措施。

Airport security has already been stepped up

Homeland Security Secretary Janet Napolitano said the measures included enhanced random任意的，随机的 screening and more air marshals执法官，司法官 on some routes.

Ms Napolitano referred to the "continued threat" from al-Qaeda.

The US had already boosted security following the attempted attack on a trans-Atlantic jet on 25 December.

A 23-year-old Nigerian, Umar Farouk Abdulmutallab, has been accused with trying to detonate引爆，爆炸 a bomb on a flight to Detroit and has been charged with the attempted murder of 290 people. He has pleaded not guilty不服罪.

Air marshals and better screening were among the measures announced by US President Barack Obama after an intelligence review last week.

'Systemic' failings

Ms Napolitano said on Thursday that the US was "taking an additional set of aviation航空 security precautions to protect the American people".

"Some of these measures include enhanced random² screening, additional federal air marshals on certain routes and adding individuals of concern to our terrorist watch list system," she said.

"As a result of these measures and others we have put in place since Christmas, travellers should allot³分配，分派 extra time when flying - particularly into the United States from overseas."

Mr Obama has criticised "systemic" intelligence failings over the plot.

Last week he announced that he had ordered an immediate⁴ strengthening of the terrorist watch list, information on security risks would be distributed分散式的 more widely, and analysis of that information would be improved.

Mr Abdulmutallab's name was on a US database of about 550,000 suspected terrorists, but not on a list that would have subjected him to extra screening or prevented him from boarding登机 a flight to the US.

He caught the flight to Detroit from the Netherlands, after connecting from a flight from Nigeria.

Al-Qaeda in the Arabian Peninsula, which is based in Yemen, claimed responsibility for the failed bomb attack.