By Martin Plaut BBC Africa reporter

The Eritrean Government has been severely criticised by the human rights organisation, Amnesty International, for unlawfully detaining dozens of political prisoners and journalists.

Amnesty says that a year ago the Eritrean authorities rounded up its most vocal critics - ranging from members of parliament to senior government officials and independent journalists.

Many of them had fought for decades for the liberation of their country - but nothing has been heard of them since.

According to Amnesty, none of those detained has been taken to court.

None have been charged with any offence, and there are increasing concerns about their health.

Charges

Some of the most serious charges were levelled against former close associates of the president.

Many Eritreans are unhappy at a lack of political freedom

Three former foreign ministers, three army generals and a vice president were accused, before the National Assembly, of committing treason during Eritrea's recent war with Ethiopia.

It was alleged that in May 2000 they offered to overthrow President Isaias Afewerki, if Ethiopia halted its offensive.

This allegation was denied by Anthony Lake one of the peace mediators, to whom the offer was supposedly made, as "utterly false".

"At no time did any Eritrean ask us to get involved in internal Eritrean politics or to pass any message to the Ethiopian Government. And of course, if they had asked us to do so, we would not have agreed," he said.

Impunity

Amnesty says it has investigated these allegations carefully and has found no evidence to support the case against the detainees, whom it declares to be prisoners of conscience.

Amnesty says the detentions not only violate international conventions signed by the Eritrean Government, they foster a climate of impunity on the part of the authorities.

Some of the journalists began a hunger strike in April this year and were then transferred from prison to unknown places of detention.

Amnesty tried to send a delegation to discuss its concerns with the Eritrean authorities, but their request for visas was turned down.