Melbourne locks up for Games

A vast security blanket will fall over Melbourne this week as jet fighters, warships and special forces deploy to back 13,000 police sealing the city to protect athletes, dignitaries and sports fans pouring in for the Commonwealth Games.

The terror alert level remains at medium - which means an attack could occur - but officials have said they have no specific intelligence of a potential attack during the Games, and the possibility of an outrage is considered low by some terror experts.

But with one man convicted under new terror laws in Melbourne last month, others awaiting trial for alleged plots to bomb key targets in both Melbourne and Sydney, and a known series of Islamic extremists supporting jihad, security agencies are taking no chances.

In the air, Air Force F/A18 Hornets will patrol a 7km exclusion zone with authority to shoot down intruding aircraft that disobey orders to leave.

On the ground, all leave for Victorian police has been cancelled, officers have been pulled into the city from outlying areas and about 5000 private security guards will help man checkpoints and entries.

They will be reinforced by a military force of about 2600, including Blackhawk helicopters, SAS troopers, commandos, a special hostage squad, bomb specialists and soldiers drafted in to help police search venues, clear waterways and check vehicles.

The Navy will station ships off Melbourne to intercept suspect vessels and protect entry to the Yarra River, which runs close to a number of venues and associated festival sites.

Regulars in a Defence Force stretched by combat deployments in Iraq and Afghanistan will be backed by civilian soldiers, part of reserve response forces set up two years ago to help counter the threat of terrorism.

Heavy security will be focused on the Queen and Prince Phillip, who will open the Games at the Melbourne Cricket Ground on Wednesday, Prince Edward and British Prime Minister Tony Blair, considered a potential target because of his commitment to the war in Iraq.

University of Melbourne terrorism expert Dr Kevin McDonald said he believed the risk of a terror attack was quite low as the Games were not associated with the centres of power that terror groups were contesting, particularly the United States.

"I think the Commonwealth Games are more a regional event and that outside the Commonwealth their profile is quite low," he said.

Former senior Australian Security Intelligence Organisation officer Michael Roach told ABC radio last year up to 60 Islamic extremists were operating in Melbourne and Sydney.

Two have so far been convicted - al Qaeda associates Jack Roche in Perth, and "Jihad Jack" Thomas, who admitted meeting Osama bin Laden and accepting A$3500 from him.

Following a series of ASIO and police raids across the country last year, two alleged terror cells were arrested.