Etihad Airways says assisting Australian police with plane attack probe

Police direct locals around a block of flats in the Sydney suburb of Lakemba after counter-terrorism raids across the city. AFP

Police direct locals around a block of flats in the Sydney suburb of Lakemba after counter-terrorism raids across the city. AFP

He told reporters in Perth that the times passengers had been advised to arrive at airports would return to normal after being extended following the alleged plot which "has been disrupted and it has been contained".

Mr Merhi was released about 7pm Tuesday and his solicitor, Moustafa Kheir, said he endured days of intense questioning.

"You need a photo ID to enter a licensed venue but not board a flight", he said.

"There's a lot of stress associated there, and not knowing, and he was shocked that he was being questioned".

On the one hand, you might get lucky and breeze through security and customs with minimal fuss, but the odds of that happening are, well. let's just say you should probably play it safe and rock up earlier. He said it had now been downgraded to "possible".

Australian Federal Police Commissioner Andrew Colvin said on Sunday an improvised explosive device was involved. "We want to review all the information police had and what basis they had to do what they did".

The houses of the detained men were still being searched on Monday evening, two days after the arrests.

Police rescue and bomb disposal squad officers late yesterday moved back into the Cleveland St, Surry Hills, home where spray painter Khaled Merhi lived.

A joint statement from the Australian Federal Police and the NSW Police Force on Wednesday morning said the investigation into the alleged plot was ongoing.

USA officials, who spoke to Reuters on condition of anonymity, said a foreign intelligence service had intercepted communications between the plotters in Sydney and members of the Islamic State militant group in Syria.

"My speculative guess is they were probably trained in how to prepare TATP", he told AAP.

He believes it may have involved the use of acetone peroxide - or TATP - the same powerful chemical used in Manchester Arena bombing in May and the 2015 Paris attacks.

Another two USA officials familiar with the Australian arrests said a developing plot had been detected.

Etihad Airways has confirmed it is helping Australian authorities with the investigation after the arrests came following a tip-off from foreign intelligence services.

Abdul Merhi was arrested in a series of police raids across Sydney, he was one of four men taken into custody.

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