Laptop bombs on planes are a matter of "when, not if", the head of the UN's counter-terrorism committee has warned.
Jean-Paul Laborde spoke to reporters after officials decided not to ban laptops from aircraft cabins on flights to the US from EU countries.
Such a ban currently applies to flights from eight other countries.
Mr Laborde also said Islamic State (IS) fighters returning to Europe would be "more dangerous" than previous waves.
IS has been losing territory in Syria and Iraq, and Mr Laborde said these fighters, originally from Europe, would be hardened from years of war. He said several European countries believe the rate of fighters returning has increased by a third over the past year.
"On average, these people are much more committed, more experienced and more skilled," he said.
"In spite of the travel restrictions, you will have a number of foreign terrorist fighters which will probably slip through the borders and go back, come back to these countries, especially with smuggling networks."
However the number of new foreign recruits going to the region is thought to be down.
The number of foreign fighters flowing to IS-controlled regions dropped by 90 percent in the past year, the US secretary of state said recently.
Mr Laborde said he did not know whether IS had the capacity to carry out a laptop bomb attack, but he was sure that organised criminal groups could.
He told a reporter from the Spanish news agency Efe that it might be "one, two or three years" but might be aided by the internet now being available on some flights.
He said he had previously identified threats two years before they occurred.
Wednesday's meeting on the matter, between US and EU officials, was requested by EU officials after recent reports suggested US authorities had new information regarding laptop parts being turned into explosives.
Details of a specific threat have not been made public.
The US restrictions, introduced in March, apply to devices "larger than a smartphone" from the cabins of flights from Turkey, Morocco, Jordan, Egypt, the United Arab Emirates, Qatar, Saudi Arabia and Kuwait.
The UK issued a similar ban on flights from six countries.
Steve Landells, a safety expert at the British Airline Pilots Association, said there was a greater risk of lithium battery fires if larger devices were kept in an aircraft's hold.