Public reaction has been muted

Those detained were among the 15 reformists who, in May this year, signed a public letter calling on President Isaisas Aferwerki government to institute democratic reforms and accountability.

The reformists had also criticised his handling of the devastating war with neighbouring Ethiopia.

Amnesty said the government should either charge them promptly or release them.

The Eritrean Government has accused the detainees of holding meetings in the United States to recruit members to join a secret opposition group.

They were also accused of planning to create secret cells to infiltrate various organisations in the country, including the Eritrean defence forces.

The BBC's Alex Last in Asmara says those abroad will face possible imprisonment if they return home.

University may open in October

Since the letter was published, one member Mohammed Blata has publicly repented for his criticism and signature of the open letter, and so he was not detained.

Our correspondent says the clampdown on the free press stems from their encouragement of open debate on political reforms in the country. He says they have often carried interviews with some of the government's critics.

So far, In Eritrea, public reaction remains muted with no public displays of support for the reformers since their arrests.

Meanwhile, the first batch of 800 University of Asmara students sent to a summer work camp in the desert have begun to return to the capital.

Another 800 are due back on Friday. A total of 2,100 were sent to the eastern lowlands , a hot arid desert by the Red Sea where temperatures reach 50C during the day.

Their stay at the work camp was extended because the students had protested against the programme.

They were also angry at the arrest of the student union president, Semere Kesete, for criticising the government's running of the university.

The university, which was due to open this week, will now resume classes on 1 October.