After cancelling the passports of 20 Sydney men, Australia’s spy agency says withholding such documents can help prevent threats to national security.

Australia’s spy agency has defended cancelling the passports of 20 Sydney men, saying such actions aid national security by preventing people taking part in terrorism acts and training.

The western Sydney men had their passports cancelled after the Australian Security Intelligence Organisation (ASIO) accused them of preparing to engage in politically motivated violence if they travelled overseas.

The Muslim men were also said to be a threat to national security because they had a “jihadi mentality”, Fairfax Media reported on Sunday.

ASIO’s move comes after Australian Federal Police (AFP) and NSW Police last week charged two men for allegedly supporting Australians fighting in Syria’s civil war.

The AFP said it believed about 100 Australians were suspected of being involved in the Syrian conflict.

ASIO says the agency can request passport cancellations on security grounds.

“Withholding passports is an important means of preventing Australians from travelling overseas to engage in activities prejudicial to national security – for example, to train, support or participate in terrorism,” the spokesperson said in a statement.

“It may also be used to help prevent an Australian already overseas from participating – or further participating – in activities that are prejudicial to the security of Australia or another country.”

Sydney lawyer Zali Burrows said up to 15 men who had their passports cancelled had approached her to act for them.

She said the men were told they were an adverse security risk but she was not aware of anyone wanting to travel to Syria to fight.

“Basically they are suspected of being terrorists or wanting to go overseas and participate in a jihad cause or for other reasons,” she told ABC radio.

Some men found out their passports had been cancelled while en route to a holiday.

“Some of these guys were just young guys wanting to go on a holiday to Bali – they even packed their boardshorts,” Ms Burrows said.

“Others even wanted to visit a sick relative.”

Last week, Sydney man Hamdi Alqudsi fronted court for allegedly organising for Australians to engage in Syria’s civil war.

Alqudsi was the alleged linchpin in a criminal group recruiting Australian men to fight with terrorist groups Jabhat al-Nursa and al-Qaeda affiliates.

The 39-year-old allegedly organised travel and contacts for seven Australians, including Amin Mohammed, who was arrested at Brisbane Airport on December 3.