Mick Keelty, the Australian Federal Police commissioner, was responding on Wednesday to claims by former Australian Security Intelligence Organisation officer Michael Roach that suspected militants were based in the two cities.
"He's close to the figure that I am aware of," Keelty told Australian Broadcasting Corp (ABC) radio, referring to Roach.
"We are focused on the people who we are aware who have trained overseas. We are focused on the people who we know have a propensity to do something wrong," he said.
Australia, a staunch US ally which sent troops to Iraq and Afghanistan, has been on a medium security alert level since shortly after the 11 September 2001, attacks on the United States, but has never suffered a major attack at home.
Roach, who retired less than two years ago after a 30-year career with Australia's domestic intelligence agency, said on Tuesday that some suspected militants in Australia were trained in explosives and reconnaissance.
"We are focused on the people who we know have a propensity to do something wrong"
Mick Keelty, Australian Federal Police commissioner
They were also trained in clandestine communications and knew how to falsify documents, he said.
"Perhaps the number is around 50 or 60 in Australia, who are working in separate cells. The threat is real. It's a matter when will this happen," Roach told ABC television.
He did not elaborate on the nature of the threat, but did say: "They are divided into groups within the cell structures, for example, having the coordinator of the group down to those people who actually will deliver the bomb."
Echoing similar proposals after the London transport bombings last month, Roach urged members of the public to report suspicious activity and even use their mobile phones to photograph or film suspicious parcels, vehicles and people.
An opinion poll published in the Sydney Morning Herald newspaper on Wednesday found that two-thirds of Australians believed the country's involvement in Iraq had made it more vulnerable to a "terrorist" attack.
The poll of 1428 people showed 87% supported the use of more security cameras, 78% wanted terrorism suspects to be deported, 66% agreed with random bag searches and 61% thought Australia should have a national identity card system.
Eighty-eight Australians were among 202 people killed in the October 2002 nightclub bombings on the Indonesian island of Bali and the Australian embassy in Jakarta was hit by a bomb in 2004.