Australia raises terror alert level to 'high' on Mideast fears

The heightened alert after years on "medium" officially means a "terrorist attack is likely".

"There are people with the intent and the capability to mount attacks here in Australia," Prime Minister Tony Abbott told a press conference.

The lifting of the threat level was "not based on knowledge of a specific attack plan but rather a body of evidence that points to the increased likelihood of a terrorist attack in Australia", Abbott added in a joint statement with Attorney-General George Brandis.

"Security and intelligence agencies are concerned about the increasing number of Australians working with, connected to, or inspired by terrorist groups such as ISIL (Islamic State), Jabhat al-Nusrah, and al-Qaeda," he said.

"The threat they pose has been increasing for more than a year."

The government believes up to 60 Australians are fighting alongside jihadists for Islamic State, while another 100 were actively working to support the movement at home.

The decision came two days after Australian police raided an Islamic centre in Brisbane and charged two men for alleged involvement in recruiting and sending jihadist fighters to Syria.

Abbott said Australians "should continue to go about their lives" despite the increased alert, although security would be heightened.

"What people will probably notice is more security at airports, more security at ports, more security at military bases, more security at government buildings and more security at public events," he said.