Soldiers with tanks laid siege to the information ministry in the capital, Amara, and forced state media to call for political prisoners to be freed.
Eritrea has been led by President Isaias Afewerki, 66, for two decades since it broke from its bigger neighbour, Ethiopia.
Soldiers forced the director-general of state television “to say the Eritrean government should release all political prisoners”, an Eritrean intelligence source said. There was no immediate statement from the government.
Last year Navi Pillay, the UN High Commissioner for Human Rights, accused Eritrea of carrying out torture and summary executions, and estimated that between 5,000 and 10,000 political prisoners were being held in the country of about six million people.
State media went off air after the call for prisoners to be freed. One Western diplomat in Ethiopia said other buildings may have been seized by soldiers too.
Eritrean opposition activists exiled in Ethiopia said there was growing dissent within the Eritrean military, especially over economic hardship. Despite its relatively small population, Eritrea has Africa’s second-biggest army.