Tanzanian opposition leader Tundu Lissu vowed to keep fighting on Monday as he appeared in court on a treason charge that carries a potential death penalty.

Activists say the case is another sign that democracy is eroding in several East African nations.

An opposition leader is also on trial for treason in neighbouring Uganda, while opposition movements face mounting pressure across multiple countries.

In Tanzania, a defiant Lissu was cheered by supporters as he entered the courtroom on Monday, surrounded by a heavy police presence.

Party disqualified from elections

Lissu's Chadema party has been disqualified from presidential and legislative elections due in October after demanding electoral reforms.

"We will be fine... Don't worry at all," he told supporters, sporting a "No Reforms, No Elections" T-shirt and brandishing a proposed draft of a new constitution.

Chadema accuses the government of President Samia Suluhu Hassan of returning to the repressive policies of its recent past.

Lissu's case was adjourned to June 2, his lawyer Rugemeleza Nshala told reporters, as the prosecution said investigations were ongoing.

'Determined to violate the law'

A group of Kenyan rights defenders, including a former chief justice, were detained at the airport in Dar es Salaam when they attempted to come and observe the trial.

That followed the similar detention and deportation of Kenyan presidential candidate Martha Karua, a former justice minister, at the same airport on Sunday.

Karua said it showed Tanzania's ruling party was "determined to violate the law and are not keen on according Tundu Lissu a fair trial".

A Kenyan government spokesperson said: "We cannot question because it is the decision of the Tanzanian government."

Pressure for opposition parties

Opposition movements face pressure across the region.

Karua also serves as lawyer for Ugandan opposition leader Kizza Besigye, who was kidnapped in Kenya in November and taken back to his home country for trial.

Uganda is due to hold elections in January.

There is also concern about the political situation in Kenya, long considered a bastion of stability in the region.

'Total disarray'

President William Ruto's popularity has been undermined by tax rises that sparked mass protests last year and were followed by a spate of abductions and political violence targeting his critics.

When Ruto's former deputy launched a new political party in Nairobi last week, unidentified attackers stormed the meeting.

Kenya is in "total disarray", Karua told AFP in an interview earlier this month.

"It's as if our constitution has been suspended. We have abductions, arbitrary arrests... extrajudicial killings... And the police and authorities fail to take responsibility," she said.

'Collaborating in erosion of democratic principles'

Karua said Kenya, Tanzania and Uganda were "collaborating" in their "total erosion of democratic principles".

"All these countries now have become dangerous, not just to others but to their own nationals. I tie this to the forthcoming elections," she said.

Meanwhile, Ethiopia's leading opposition party, the Tigray People's Liberation Front, was banned from any political activity last week, ahead of elections due by June 2026.

South Sudan has repeatedly delayed holding its first elections and President Salva Kiir has placed his long-time rival, First Vice-President Riek Machar, under house arrest.

Rwandan President Paul Kagame last year won re-election with more than 99% of the vote, amid long-running accusations of repression targeting the opposition.