Airport security officers have detained five terrorism suspects, as the government awaits a US approach for military action in Iraq and Syria.

Five people suspected of terrorist links have been pulled off flights at Australian airports as part of a security crackdown.

The revelation came as Prime Minister Tony Abbott laid out the steps he would take if the United States formally asked Australia to take part in military action in Iraq and Syria to stop the rise of Islamic State extremists.

Parliament was told on Thursday that five suspects had been detained and questioned, including two in the past week when new anti-terrorism units began working at the Sydney and Melbourne international airports.

It is understood the two men questioned in Sydney and Melbourne had been heading to Beirut and both were carrying images of Islamic State activities such as beheadings, which by law is considered objectionable material.

One was carrying a large sum of cash, reportedly up to $30,000.

“We have changed the setting on our borders … (and) instructed our officers to place national security above passenger facilitation,” Immigration Minister Scott Morrison told parliament.

Air passengers would regrettably be inconvenienced, but the government valued “vigilance over convenience”.

An extra 80 anti-terrorism officers will be added to the 1300 stationed at 40 airports.

ASIO says 15 Australians, including two suicide bombers, have been killed in renewed fighting in Iraq and Syria and 60 are still on the battlefield.

Mr Abbott said Islamic State was “as near to pure evil as we are ever likely to see”.

Australia had not yet received a formal approach from the US to take part in a new coalition mission in Iraq or Syria.

Should it do so, the government would want to look at any request in the light of achievable objectives, a clear role for Australian forces, a full risk assessment and an overall humanitarian objective, the prime minister said.

“No one in this parliament would wish to stand by and watch the preventable slaughter of innocent people.”

Mr Abbott said he appreciated Labor’s bipartisan support for the government’s actions, including proposed new anti-terrorism laws.

However, Opposition Leader Bill Shorten was forced to pull caucus members into line over comments that the government was using national security for political points.

Senator Sue Lines said the issue was a “shield to try and deflect from the awful mess they’re in with their budget”.

Labor frontbencher Kim Carr appeared to back up his colleague.

“What we see from this government is that they want to talk about everything but (the budget),” he said.

Mr Shorten, who spoke with Senator Lines after the comments, said Labor recognised that national security was above day-to-day politics.