Image caption A violent protest sprang up outside Bagram base as news of the incident spread

US Defence Secretary Leon Panetta has apologised to the Afghan people for an incident in which copies of the Koran were reportedly burned.

Mr Panetta said the US military respected the religious practices of the Afghan people "without exception".

The Nato commander in Afghanistan, US Gen John R Allen, has already announced an inquiry into the incident.

Reports suggest the US had confiscated materials that they suspected Taliban prisoners were using to send messages.

News of the incident has triggered angry protests outside the US base at Bagram, north of Kabul.

One person was wounded and five were detained when Nato forces used rubber bullets to disperse the crowd.

"This morning Gen Allen notified me of the deeply unfortunate incident involving the inappropriate treatment of religious materials, including the Koran, at Bagram Airbase," a statement from Mr Panetta said.

"He and I apologise to the Afghan people and disapprove of such conduct in the strongest possible terms.

Analysis The US military is in full damage-limitation mode, with Gen Allen making two contrite television apologies. Afghan security forces have been put on alert nationwide amid fears of a repeat of the bloodshed that followed news of a Koran being burnt last year in the US. This latest incident may have begun with the Americans uncovering a secret message system between suspected Taliban prisoners. The Americans confiscated the Korans and other religious documents because they believed prisoners were using them to hide messages to each other, two senior Afghan officials told the BBC. A military official familiar with the investigation gave a similar account, but it's still not clear why the Americans would then burn these books.

"These actions do not represent the views of the United States military. We honour and respect the religious practices of the Afghan people, without exception."

Mr Panetta said he supported Gen Allen's decision to launch an inquiry.

"I will carefully review the final results of the investigation to ensure that we take all steps necessary and appropriate so that this never happens again," he said.

Afghan President Hamid Karzai condemned the reports that the Koran had been burnt. The Taliban said the incident would hurt the feelings "of one billion Muslims around the world".

Reports said the Korans had been found in piles of rubbish that Nato had transported in a lorry on Monday night to a pit on the base where waste is burned.

Afghans working at the pit are believed to have seen the religious books and stopped the disposal process.

Two senior Afghan officials told the BBC that religious materials held by Taliban prisoners had been confiscated because US officials suspected they were using them to send secret messages to each other.

'Not intentional'

Gen Allen said that any "improper disposal" of religious materials had been inadvertent.

Previous tension points January 2012: US and UN officials describe a video clip of US marines urinating on dead Afghans as "disgusting" and "inhuman"

April 2011: US President Barack Obama describes March 2011 Koran burning by a radical US pastor as "intolerance and bigotry". The incident triggered protests which left at least 24 people dead in Afghanistan

April 2008: Dutch and Danish governments evacuate their embassies in Kabul after protests against cartoon of the Prophet Muhammad which was reprinted by Danish newspapers 'Rebranding' US detention in Afghanistan

"We are thoroughly investigating the incident and we are taking steps to ensure this does not ever happen again. I assure you… I promise you… this was not intentional in any way," he said.

Witnesses said that about 2,000 protesters gathered outside the base as word of the incident spread.

"We Afghans don't want these Christians and infidels, they are the enemy of our soil, our honour and our Koran," said one protester, Haji Shirin.

"I urge all Muslims to sacrifice themselves in order to pull out these troops from this soil."

Bagram includes a prison for Afghans detained by Nato forces.

Some Afghans claim inmates there have been ill-treated and Mr Karzai has demanded that those detained be transferred to Afghan security.

Nato and Afghan security forces have been put on alert over fears of a repeat of violence that followed news of a Koran being burnt last year by a hardline preacher in Florida. At least 24 people in Afghanistan died in angry protests triggered by that incident.