AFP boss confident in airport security

The Australian Federal Police boss says travellers should be "very confident" in the security at Australian airports.

AFP Commissioner Andrew Colvin says state and federal officers have increased their presence at airports around the country since the arrest of four men in Sydney on the weekend suspected of plotting to blow up a plane.

"We have very good security at airports now," he said on Monday.

"What we are doing, what you're seeing at the moment is making sure there is extra vigilance, to make sure we aren't cutting any corners in our security.

"This is not stagnant though and we are always reviewing what the best arrangements are."

Mr Colvin said any delays to travellers were justified.

"It's a small inconvenience for what is an incredible benefit," he said.

Mr Colvin remained tight-lipped on details of the investigation into the four men who are being held under special terrorism powers after being arrested during counter-terror raids on Saturday night.

He would not confirm reports the alleged plot may have involved a crude bomb disguised as a kitchen meat grinder, or a plan to release poisonous gas inside the plane.

He also refused to confirm whether the attack was targeting a domestic or international flight.

"The plot that we are investigating we believe was an attempt to put a device onto an aircraft, but beyond that the speculation is just that - speculation," Mr Colvin said.

"Until we finish our investigation, until we know which of our many working theories we have, and until we can put that information before the courts it's not helpful to keep speculating."