France's Prime Minister has said there is an "urgent" need to tighten controls on the European Union's borders after bombings in Brussels that left 31 dead were claimed by the so-called Islamic State group.
Manuel Valls told French radio that heightened vigilance was required to stop people crossing into Europe with false passports, as IS has "stolen a large number of passports in Syria."
Europe is facing a security crisis after the Brussels attacks and those in Paris in November which revealed jihadists were easily moving between member states, several of them returning from battle in Syria.
Two of the suicide bombers involved in the Paris attack - which left 130 dead - were found with fake Syrian passports and several crossed into Europe posing as refugees.
Mr Valls again urged the adoption of a Europe-wide system of tracking airline passenger names, which has led to misgivings among some over the use and security of personal data.
France has led the calls for adopting the Passenger Name Record system first mooted in 2010, which would cover all international and internal EU flights while providing safeguards on access to and use of the data collected.
Man detained in Brussels not prime suspect
Several countries have tightened or reviewed airport security following the attacks in Brussels, as Australian Prime Minister Malcolm Turnbull blamed Europe's porous borders and lax security for the attack.
Mr 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 is tighter at airports around the world this morning, with many countries saying they were deploying additional resources at major transport hubs.
New measures included increased checks on those entering terminals and additional patrols within terminal buildings, officials said.
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 today.
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 bomb in October last year.
IS claimed responsibility for smuggling the bomb on board.
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.