The lawyer for a man arrested over an alleged plot to attack a plane — then released without charge — has said he wants to know why police arrested his client, adding that it had "caused a lot of damage to him".

Key points: One of four men arrested over alleged plane attack released from custody on Tuesday night

One of four men arrested over alleged plane attack released from custody on Tuesday night Abdul Merhi, 50, released without charge, but his lawyer "will review police action"

Abdul Merhi, 50, released without charge, but his lawyer "will review police action" The four reportedly have deep connections to Islamic State

Four men were arrested by the New South Wales Joint Counter-Terrorism team on Saturday after intelligence reports of a plot to take down a passenger plane using an improvised device.

One of them, Abdul El Karim Merhi, 50, was released from police custody in Sydney about 7pm on Tuesday night.

On Wednesday morning his lawyer Moustafa Kheir tweeted: "My client Abdul Merhi has been released without charge. Tough few days, but he's relieved the truth is out. I will review police action."

Mr Kheir told AAP that Mr Merhi underwent days of intense questioning.

"It's a very serious allegation to have against you," he said.

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

Police smashed a door at a Punchbowl unit block when they arrested Abdul El Karim Merhi on Saturday. ( ABC News: Jessica Kidd )

"It's just unfathomable that he would be associated with anything like this."

Mr Merhi's family was also in shock and his life had been "turned upside down", Mr Kheir said.

"He just wants to go back to as normal life as possible now."

Loading

Mr Kheir said he would review the actions of police.

"A lot of information was divulged, including his identity," he said.

"That's caused a lot of damage to him. We want to review all the information police had and what basis they had to do what they did."

The alleged conspiracy to smuggle the bomb onto a flight, hidden in a meat grinder, was uncovered after a tip-off from a foreign intelligence agency.

On Monday 7:30 reported that the four men who were arrested — Khaled Khayat, Mahmoud Khayat, Abdul El Karim Merhi and Khaled Merhi — have deep connections to Islamic State.

A further three men remain in custody without charge at the Sydney Police Centre in Surry Hills.

Terrorism suspects can be detained and questioned without charge for an extended period under special provisions in the Crimes Act.

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.

Khaled Khayat (L) and Mahmoud Khayat were arrested by police as part of their counter-terrorism raids in Sydney on July 29. ( Supplied )

'Islamist extremist motivation' behind alleged plot

Officers carried out a series of raids in Surry Hills, Wiley Park, Lakemba and Punchbowl on Saturday afternoon and have spent the last few days scouring for evidence of the alleged plot, including items that could have been used in a homemade bomb.

A man is arrested on Sproule Street Lakemba, as part of raids across Sydney on Saturday. ( Supplied: Braden Kerr )

It is not yet known what type of plane the group allegedly wanted to target or when they intended to carry out the attack.

Two cars were towed near the scene of police investigations in Surry Hills on Wednesday afternoon.

Cars were towed in Surry Hills as police investigate alleged terrorist activities. ( ABC News: Jackson Vernon )

A blue tarp was also put over two backyard garages.

Justice Minister Michael Keenan has said it was "quite a sophisticated plot".

"It was a plot to bring down an aircraft with the idea of smuggling a device on to it to enable them to do that," he said.

Prime Minister Malcolm Turnbull said the plans were "advanced" and allegedly fuelled by "an Islamist extremist motivation".

"Police will allege they had the intent and were developing the capability," he said.