Scores of parliamentarians, journalists, army officers and civilians arrested since the beginning of the month by the Chadian authorities must either be charged with recognizable crimes or immediately released, Amnesty International said today.

Since an alleged coup attempt on 1 May in which eight people were reportedly killed in unclear circumstances, activists and journalists have been targeted in a wave of arrests, detentions, harassment and intimidation across the capital N'Djamena.

Most of those detained have been refused visits from family members, lawyers or doctors. Some are believed to be held incommunicado.

"The growing wave of arrests and detentions in N'Djamena is extremely troubling, particularly given that we still don't know the identities and whereabouts of all those held," said Christian Mukosa, Chad researcher at Amnesty International.

"Detaining all those who speak up against the government is not the best way to prevent political turmoil in Chad. The authorities need to ensure those held are either formally charged or released and that speaking out is not punished in the country."

Journalist Eric Topona, Secretary-General of the Union of Chadian Journalists (Union des Journalistes Tchadiens, UJT), was arrested on 6 May after he went to the N'Djamena Magistrate's Court in response to a summons issued by an investigative judge.

He was later charged with "endangering constitutional order", detained and transferred to Am Sinene detention centre in the suburbs of the city.

According to his lawyer, Topona was summoned to testify in a defamation case against author and activist Jean Laoukolé.

In another case, on 7 May Moussaye Avenir De La Tchiré, editor in chief of Abba Garde newspaper and the UJT's treasurer was arrested by a group of men in civilian clothes while he was in his car in the Dembé suburb of N'Djamena.

The men forced him into their vehicle and drove to an unknown location. He was found on 8 May in a former military camp in N'Djamena known as "Camp OCAM" in Moursal suburb. He has not been charged yet.

Also on 7 May, police in the Senegalese capital Dakar arrested Chadian blogger Makaila Nguebla, who had fled his country a few years earlier and was now living in Senegal.

He was arrested when he went to a police station in Dakar in response to a summons by a police commissioner. He was accused by the Senegalese police officer who questioned him of communicating by email with activists including Eric Topona and "raising the population against the Chadian government using social media".

On 1 May, a number of opposition members of parliament were also arrested and some of their homes were searched. Two other MPs were arrested in the evening of 8 May.