Berlin/Sydney. Several countries have tightened or reviewed airport security following twin explosions at Brussels Airport, as Australian Prime Minister Malcolm Turnbull on Wednesday (23/03) blamed Europe's porous borders and lax security for the attack.
Islamic State claimed responsibility for the bomb attacks in the departure hall of Zaventem airport, and a rush-hour metro train which killed at least 30 people.
Prosecutors said the blasts at the airport, which serves more than 23 million passengers a year, were believed to be caused by suicide bombers.
Turnbull waded into the global debate about protecting borders, reassuring Australians that "our domestic security arrangements are much stronger than they are in Europe where regrettably they allowed things to slip".
"That weakness in European security is not unrelated to the problems they've been having in recent times," he said in Sydney.
Security was tighter at airports around Asia on Wednesday, with South Korea, Japan, Indonesia, Thailand and India saying that they were deploying additional resources at the major hubs.
New measures included increased checks on those who were entering terminals and additional patrols within the terminal buildings, said officials from around the region.
In India, where airport security is tighter than in most parts of Asia, only passengers with a valid flight ticket and passports were allowed to enter the terminal buildings before Tuesday's attacks.
After Brussels, the country has begun to check some of the bags that the passengers bring into the terminals, said Surender Singh, the director general of the Central Industrial Security Force, which is in charge of security at commercial airports.
But he ruled out checking every bag that goes into the terminals, saying that security forces needed to balance security with passenger conveniences.
"It will not be possible at the moment. It would require a whole lot of changes at the airport itself," said Singh. "With hundreds of passengers lined up at Delhi airport, 100 percent checking of everybody and it would come to a standstill."
Authorities in London, Paris and Frankfurt responded to the attacks by stepping up the number of police on patrol at their airports and other transport hubs. Airlines scrambled to divert flights as Brussels airport announced it would remain closed on Wednesday.
In the United States, the country's largest cities were placed on high alert and the National Guard was called in to increase security at New York City's two airports.
A United Nations agency was already reviewing airport security following the downing of a Russian airliner in Egypt by a makeshift soda-can bomb in October last year. Islamic State has claimed responsibility for smuggling the bomb on board.
But despite attacks like a suicide bomb at Moscow's Domodedovo airport's arrival hall in 2011 that killed 37 people, there has been less attention focused on how airports themselves are secured.
"It strikes me as strange that only half of the airport is secure. Surely the whole airport should be secure, from the minute you arrive in the car park," said Matthew Finn, managing director of independent aviation security consultants Augmentiq.
The relative openness of public airport areas in Western Europe contrasts with some in Africa, the Middle East and Southeast Asia, where travelers' documents and belongings are checked before they are allowed to enter the airport building.
In Turkey, passengers and bags are screened on entering the terminal and again after check-in. Moscow also checks people at terminal entrances.
Israel's Ben Gurion Airport is known for its tough security, including passenger profiling to identify those viewed as suspicious, bomb sniffing devices and questioning of each individual traveler.
In the Kenyan capital Nairobi, where authorities are on high alert for attacks by Somali-based al Shabaab militants, passengers have to get out of their cars, which are then searched, at a checkpoint a kilometer from the main terminal.
But adding checks such as bag X-rays at terminal entrances could themselves create a potential target, one analyst said.
"Any movement of the security 'comb' to the public entrance of a terminal building would cause congestion, inconvenience and flight delays, while the inevitable resulting queues would themselves present an attractive target," said Ben Vogel, Editor, IHS Jane's Airport Review.