The family are calling for the release of Omar Deghayes

Amani Deghayes, of Kilburn, London, said she depended on journalists and lawyers for information about her brother, Omar, 36, a British resident.

She said she feared for his life and worried how long his body could cope.

The hunger strike was called after it was claimed officials had reneged on agreements. Some strikers have eaten and some are having medical assistance.

Ms Deghayes said her brother had been beaten and tortured during interrogation.

"No officials have come forward to answer what evidence there is," she told BBC Southern Counties Radio.

They had a small child, a three-month-old son who is now four and doesn't know his dad Amani Deghayes

"There is no formal charge as far as I know. This is what is so frustrating - they are held there and there is no forum to challenge what they have."

She said information was scare and the family was left to rely on the internet and investigative journalism such as a recent Newsnight programme which found the training video her brother was said to have been involved in.

"It was very obvious to us it was not him," she said.

She said Omar had gone to Afghanistan to find out the truth for himself about a "controversial" country.

"My father is a lawyer. We have been brought up to go and see things for ourselves and make our own decisions rather than receiving whatever the media or other people say," she said.

Assisted feeding

Ms Deghayes, 30, said her brother met and married an Afghan woman while he was there.

The couple fled to Pakistan, the nearest safe country, when war broke out but he was detained by US soldiers.

"They had a small child, a three-month-old son who is now four and doesn't know his dad," Ms Deghayes said.

Her brother has been held at the US military base in Cuba since 2002.

The Foreign Office has said the government does not have legal responsibility for a non-British subject.

Mr Deghayes who was born in Libya and was educated in the UK had applied for British citizenship.

After it was revealed that the hunger strike had entered its second month, prison officials said 87 inmates were still taking part in the strike and 10 were being fed through nose tubes.

Brighton MP Des Turner told the BBC the Guantanamo Bay prisoners had a basic human right which was "not to be detained without being charged or tried".

He said: "If the US really think they have serious evidence against these people they should charge them and try them by proper process of law and in the meantime they should be kept in civilised prison conditions."

He said he was lobbying the Foreign Office to exert pressure on behalf of Mr Deghayes.