Petraeus resigned last week to pre-empt revelations of an affair with his married biographer Paula Broadwell, bringing to an end a glittering military career that included a spell commanding NATO forces fighting the Taliban in Afghanistan.

A Taliban official burst into laughter at the mention of the Petraeus affair during an interview with AFP in northwest Pakistan this week.

"What a bastard! But all Americans are the same, it's nothing new," the official said, who did not want to be named.

The traditional moral code of the Pashtuns also demands severe punishment for adulterers.

"From a Pashtun point of view, Petraeus should be shot by relatives from his mistress's family," the Taliban official explained.

"From a sharia point of view, he should be stoned to death."

Petraeus, a four-star general married for 37 years, stepped down as head of the US spy agency just three days after President Barack Obama's re-election over his fling with Broadwell, an army reservist who travelled to Afghanistan to write a glowing biography of the general.

The scandal has also implicated the current NATO commander in Afghanistan, General John Allen, as well as an FBI agent and a glamorous Florida socialite.

The Taliban official said he was not surprised.

"It's quite normal for Americans and Western people to behave like this -- they live in free sex societies where nobody cares about this sort of thing, so what do you expect?" he said.