Al Qaeda and groups linked to it remain the world's biggest security threat despite the killing of Osama bin Laden, the head of Interpol said on Tuesday.
Airlines and other forms of public transport are most at risk, with terrorists using fraudulent passports to travel undetected an area of particular concern, Interpol secretary general Ronald Noble told reporters on the sidelines of an aviation meeting in Singapore.
"Even before bin Laden was captured and killed, the biggest threat was not only al Qaeda but al Qaeda-affiliated terrorist groups around the world," he said "I think that remains the biggest threat now as it was before his death.
"The airline and air industry continues to be a prime target for terrorists, but we've seen from recovered intelligence etc that they are also focusing a lot on mass transit. But airlines continue to be a special target."
A major worry, he said, was the use of stolen or missing passports and the fact that many countries did not match passports of passengers to a database of missing documents.
"One out of every two international air arrivals is not being screened. That's almost half a billion each year not being screened," Noble said.
"We know if terrorists can move from country to country without being detected, that's a risk to all countries, and from Interpol's perspective that is a number one risk affecting all countries throughout the world."
He said security agencies screened 490 million passports in 2010 and identified 40,000 of them as being listed as stolen or missing.
Interpol's database, he said, contained details of 16 million missing passports and 12 million missing national identity papers.
"Each country should focus on those individuals they know the least about, which tend to be non-nationals," Noble said.
"So the focus of each country should be get as much information as possible about non-nationals when they come to their countries so they can decide whether or not to issue a visa. And they do that by checking identity documents and sharing information through their intelligence services, through their police and through Interpol worldwide."