Malcolm Turnbull says counter-terrorism agencies have foiled a plot to “bring down” a plane in a terrorist attack in Australia.

Four men were arrested on Saturday night when heavily armed counter-terrorism officers raided four Sydney properties over an alleged plot to blow up an aircraft.

The prime minister said increased security measures have been placed on all Australian airports.

The Australian federal police commissioner Andrew Colvin said officers became aware people in Sydney were planning to commit a terrorist attack using an “improvised device”.

Commissioner Colvin said the four men in custody had not been charged by police.

Police believed the attack would target the Australian aviation industry at a major airport.’

Saturday’s raids on properties in the inner-city suburb of Surry Hills, and in Lakemba, Wiley Park and Punchbowl, were carried out by the joint counter-terrorism team, which “relate to an ongoing investigation”.

As many as 40 riot squad officers were seen at a house in Surry Hills. Drivers were told to avoid the area between Elizabeth and Crown streets.

Television footage showed a man with a bandaged head being led away by officers, wrapped in a blanket.

The prime minister said he was being briefed on the operation’s progress by security agencies.

“My number one priority, and that of my government, is the safety and security of all Australians, and the public should be reassured that our security and intelligence agencies are working tirelessly to keep us safe,” Turnbull said.

Australia, a staunch ally of the US, has been on heightened alert for attacks by homegrown militants returning from fighting in the Middle East, or their supporters, since 2014.



Authorities say they have thwarted a number of potential attacks since then, but several “lone wolf” attacks have occurred, including a December 2014 cafe siege in Sydney that left two hostages and the gunman dead.

In June, Melbourne police raided five addresses after a man killed a building clerk, took an escort hostage and injured three officers, before dying in the shootout with police.

In February, police arrested a 42-year-old electrician following a raid on his house in connection with supporting Islamic State.

About 100 people have left Australia for Syria to fight alongside organisations such as Isis, Australia’s immigration minister, Peter Dutton, has said.

Australia’s National Terrorism Threat Advisory System lists the threat level as “probable”, the third-highest measure, while the UK foreign office advice says terrorists are “very likely” to try to carry out attacks in the country.

In September 2014, the biggest counter-terrorism raids in Australian history led to 15 people being detained.

• On 31 July 2017 this article was corrected. A previous version wrongly said a man in Melbourne killed an escort he had taken hostage.