Passengers facing delays as US requests extra airport screening

But across Europe there are few visible changes on the ground at large hubs such as London, Paris, Amsterdam and Frankfurt, which alone

account for 20-30 daily trans-Atlantic flights each.

The US has said anyone travelling from or through nations regarded as state sponsors of terrorism – as well as "other countries of interest" –will now be required to go through enhanced screening, including full-body pat-downs, carry-on bag searches, full-body scanning and explosive detection technology.

The US State Department lists Cuba, Iran, Sudan and Syria as state sponsors of terrorism. The other countries whose passengers will face enhanced screening include Afghanistan, Algeria, Iraq, Lebanon, Libya, Nigeria, Pakistan, Saudi Arabia, Somalia and Yemen.

The measures follow the arrest of Nigerian man Umar Farouk

Abdulmutallab who tried to set off a bomb on a flight from Amsterdam to Detroit on Christmas Day.

In Jordan, a key Western ally, security was beefed up at Amman's main international airport since the Christmas Day bombing attempt. An official at Queen Alia International Airport said "enhanced techniques" were being applied, especially in screening passengers bound for the US.

Pakistan's national airline is intensifying security checks for US-bound passengers, even though there are no direct flights to the States from Pakistan. Screening was also stepped up for those flying to the US from other parts of Asia and the Middle East.

In South Korea, an official at Seoul's Incheon International Airport said US-bound passengers now had to go through additional security before boarding.

The Australian Transport Ministry said all passengers flying to the US would continue to be patted down and have all their cabin luggage searched.

In Abu Dhabi, British Airways passengers were delayed yesterday

following a customer complaint about lax airport security.

All the passengers on the London-bound aircraft had to disembark and go through security again. The plane was also searched after a woman passenger had reportedly told the captain that she was unhappy with the level of security at Abu Dhabi.

The plane, which had stopped at Abu Dhabi having taken off at Muscat, eventually arrived late at Heathrow airport in London.

Meanwhile, two suspected al-Qaida terrorists were killed in clashes outside the Yemeni capital Sana'a yesterday as the US and British embassies remained closed for a second day by terror threats.

The fighting was in a region where the government last month raided an al-Qaida cell it said was plotting attacks against foreigners.

In yesterday's clashes troops attacked a group including Nazeeh al-Hanaq, a senior figure on Yemen's most wanted list, as they moved through the mountainous area of Arhab. Al-Hanaq escaped, but two fighters with him were killed.

Yemen has carried out a string of raids on al-Qaida hideouts in the past month, part of an intensified effort to stamp out its growing presence.