Troops detained thousands of people during the crackdown

Win Shwe was arrested on 26 September near Mandalay, as the government began its bloody crackdown on the protesters.

The National League for Democracy (NLD) member died during questioning, the Thailand-based Assistance Association for Political Prisoners (AAPP) said.

His death raises fresh concerns for the hundreds of people still in custody.

The 42-year-old activist died "as a result of torture during interrogation", the AAPP said.

"His body was not sent to his family and the interrogators indicated that they had cremated it instead."

Sources close to Win Shwe confirmed to the BBC that officials had come to tell his family of his death and had not returned his body. He had a heart condition, they said.

The White House has demanded an investigation into his death.

"The United States strongly condemns the atrocities committed by the junta and calls for a full investigation into the death of Win Shwe during his detention in Burma," spokesman Gordon Johndroe said.

UN statement

Thousands of people were arrested last month when the military used force to end days of anti-government protests in the main city, Rangoon, and other towns and cities around the country.

Ten people died and about 1,000 are still being held, the government says, but foreign diplomats and analysts fear both figures could be far higher.

Than Shwe has offered conditional talks with Aung San Suu Kyi

The BBC's South East Asia correspondent, Jonathan Head, says the military operates a network of about 80 prisons and interrogation centres and some 60 labour camps.

Conditions in them are known to be atrocious, with torture routinely used on the prisoners, our correspondent says.

The government has faced strong international condemnation for its actions and has in recent days taken what could be conciliatory steps.

It has appointed a liaison officer to hold talks with the NLD's leader, Aung San Suu Kyi, who is under house arrest.

Burma's top General Than Shwe has also offered talks - but only if she agrees to drop what he called her "confrontational attitude".

Correspondents say many Burmese are sceptical of the regime's sincerity, and believe the offer of talks is just a delaying tactic until international pressure fades away.

At the United Nations, Security Council members the US, UK and France are pushing to agree a statement condemning the military crackdown and calling for prisoners to be released.

But the language of the statement has had to be watered down after objections from China, which is Burma's main trading partner.

Both China and Russia argue that the violence in Burma is an internal issue that does not threaten regional peace.