Afghanistan's Taliban called on US people to put pressure on their government over the capture of a US soldier, saying in an internet message that Washington could not win the war despite its modern weaponry.

"We call on the US people to see the tape of their captured soldier and listen to what he says," said the Taliban statement, an Arabic translation of which was posted on Islamist websites.

"Let them make serious and productive efforts toward ending his detention," it said.

In a video released by the Taliban at the weekend the captured soldier, named by the Pentagon as private Bowe Bergdahl, 23, said he was scared and missed his family.

Prompted by his captors, he said US citizens had "the power to make our government bring them (troops) home."

"We witness a power that is drunk on its advanced technology and modern equipment ... whose efficacy has been destroyed and made worthless by God against the mujahideen (holy war fighters) in Afghanistan," said the Taliban statement, dated July 20.

The US military Sunday denounced the Bergdahl video as Taliban propaganda that violated international law.

Thousands of US and British troops have launched offensives in Helmand province as part of US President Barack Obama's new strategy to combat the Islamist insurgents.

The southern province is a Taliban stronghold and the major producer of opium that funds their insurgency.