A former high-ranking United States defence official says Australian troops could be in Afghanistan for the next 30 years.

Australia's strategy in the country has been thrust back into the spotlight this week with the deaths of two Australian Army engineers in Uruzgan province.

Defence Minister John Faulkner says Australian troops are likely to be in Afghanistan for the next three to five years as part of the US-led effort against a resurgent Taliban.

But former US strategic analyst Daniel Ellsberg has warned that the war is not even half-way through.

Mr Ellsberg exposed how four successive US adminstrations lied to the public about the Vietnam War when he leaked the top-secret 'Pentagon Papers' to the New York Times in 1971.

"For Australian troops I think that three to five years is not just a conservative estimate, it's totally foolish," he told Radio National this morning.

"The war will no more be over in three to five years than it is right now.

"If Australians are committed to supporting this strategy they can figure on 10, 20 and 30 years."

Mr Ellsberg says the recent deployment of 30,000 US troops is unlikely to be the last such deployment.

"[President Barack Obama] has claimed that he proposes to remove troops in 18 to 22 months, but I think the impression that the troops deployed there represent a glass ceiling is totally false, just like it was during the Vietnam War," he said.

There was more bloodshed in Afghanistan overnight, with at least 39 people reported dead in a suicide bomb attack on a wedding near Kandahar, and four US soldiers killed when their helicopter was shot down by insurgents in the south of the country.