The reason for the detentions was not immediately clear. A police spokesperson did not immediately respond to a Reuters request for comment.

President Samia Suluhu Hassan says the government is committed to respecting human rights and ordered an investigation into a series of abductions last year, when several government critics were kidnapped and injured or killed by unknown people.

Lissu, who was runner-up in a presidential election in 2020, was charged with treason this month over what prosecutors said was a speech calling on the public to rebel and disrupt presidential and parliamentary elections that are expected to take place in October.

He was not allowed to enter a plea on the treason charge, but pleaded not guilty to a separate charge of publishing false information. Days later, the country’s election commission disqualified CHADEMA from taking part in the elections, on the grounds it failed to sign a election code of conduct on time.

The party, which has called this unconstitutional, had previously threatened to boycott the elections unless significant reforms were made to an electoral process it says favours the ruling party.

The charges against Lissu, who survived being shot 16 times in 2017, have placed Hassan’s human rights record under the spotlight as she seeks re-election.