The US Transportation Security Administration (TSA) said in a statement: "… every individual flying into the US from anywhere in the world travelling from or through nations that are state sponsors of terrorism or other countries of interest will be required to go through enhanced screening.

"The directive also increases the use of enhanced screening technologies and mandates threat-based and random screening for passengers on US bound international flights," the US agency responsible for air security measures said.

The US currently lists Cuba, Iran, Sudan and Syria as "state sponsors of terrorism" but the air travel directive also includes Afghanistan, Algeria, Iraq, Lebanon, Libya, Nigeria, Pakistan, Saudi Arabia, Somalia and Yemen, the Reuters news agency cited an Obama administration official as saying.

'Discriminatory' measures

However, Nigeria criticised the measures as discriminatory.

"It is unfair to include Nigeria on the US list for tighter screening because Nigerians do not have terrorist tendencies," Dora Akunyili, Nigeria's information minister, said.
  

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"It is unfair to discriminate against over 150 million people because of the behaviour of one person."

Chris Yates, an aviation security specialist, said that wider measures were needed to improve security on US-bound airliners.

"We need to be looking at all high-risk flights, irrespective of where they come from or where they are going to, and apply the approriate measures to all passengers effectively rather than singling out a small group of nations," he told Al Jazeera from Manchester.

"The system has to be a system of systems.

"On the one hand we are talking about technology, but we are also talking about technique as well - profiling, additional security equipment that will give us that greater capability to detect something that we really wouldn't like to see onboard." 

London's Heathrow airport – Europe's busiest – is the latest airport to say it is looking at introducing full body scanners to screen passengers in light of the attempted attack.

Gordon Brown, the British prime minister, said on Sunday the authorities were acting "quickly" to introduce the new measures because a new form of explosive used by al-Qaeda "is not being identified by ordinary machines".

"They [passengers] will see checks for explosive traces – that will be done on hand luggage. Transit passengers will also be checked as well as transfer passengers," he said, adding that he hoped it would not lead to longer queues at airports.

The Netherlands announced on Wednesday that body scanners would be used on all flights from Amsterdam's Schipol airport to the US.

Security alert

Meanwhile, a security alert shut down a terminal at Newark International Airport in the US for several hours.

The New Jersey airport's Terminal C was cleared after an unidentified man managed to bypass a security checkpoint on Sunday. Flights were grounded during the lockdown.

"TSA immediately halted screening at Terminal C's security checkpoints and worked with law enforcement to pull airport surveillance tapes to identify the individual in question," Ann Davis, the agency's spokeswoman, said in a statement.

Passengers were allowed to begin boarding again about six hours later, but officials said the man who had caused the alert had not been found.