Security is being stepped up at airports around the world amid fears of a possible attack by Islamic militants who have been fighting in Syria and Iraq.

A number of countries have been asked by the US to implement extra security measures for direct flights to America.

There are concerns two terror networks are working together on a bomb that could evade existing measures.

US Homeland Security chief Jeh Johnson said he had tasked officials to "implement enhanced security measures in the coming days at certain overseas airports with direct flights to the United States".

However, he declined to specify which airports would be subjected to the extra security measures.

But the Dublin Airport Authority (DAA) says they are working with the Department of Transport closely - but there will be no direct effect on passengers for the moment.

A statement issued by the US Department for Homeland Security said "We are sharing recent and relevant information with our foreign allies and consulting the aviation industry".

"These communications are an important part of our commitment to providing our security partners with situational awareness about the current environment and protecting the travelling public".

US officials said the move was due to intelligence reports that Islamist groups in Yemen and Syria had joined forces to prepare an attack on the US.

Bomb-makers from al-Nusra Front, al-Qaeda's affiliate in Syria, and Yemen-based al Qaeda in the Arabian Peninsula (AQAP) are believed to be working together to develop the devices.

The enhancements are likely to include added scrutiny of US-bound passengers' electronics and footwear, and installation of additional bomb-detection machines.

ABC News has reported that the explosives these operatives are attempting to build include non-metallic bombs that could evade metal detectors.

Aviation journalist Gerry Byrne told Newstalk Breakfast what all this could mean.