Leading Kenyan lawyer and the country's former Justice Minister, Martha Karua, says she has been deported from Tanzania to prevent her from attending the court case of opposition leader Tundu Lissu.

Two colleagues accompanying her were also reportedly detained and deported after flying in from neighbouring Kenya. Tanzanian authorities have not yet commented.

Lissu, who is the leader of Tanzania's main opposition Chadema party, is due to appear in court on Monday after being charged with treason last month.

Karua is a respected human rights advocate and a vocal critic of what she calls "democratic backsliding" in East Africa.

She has also been representing Ugandan opposition politician Kizza Besigye, who was kidnapped in Kenya last year and taken back to his home country to face treason charges.

Like Lissu, he denies the charges, arguing that they are politically motivated.

Karua served as Kenya's justice minister from 2005 to 2009, and was the running mate of former Prime Minister Raila Odinga in his failed presidential bid in elections in 2022.

She launched her own opposition party, the People's Liberation Party (PLP), earlier this year.

The PLP said that she, along with fellow Kenyan lawyer Gloria Kimani and human rights campaigner Lynn Ngugi, were subjected to "hours of unwarranted interrogation", before being deported.

Condemning the incident, Chadema general secretary John Mnyika said: "The solution to hiding the shame of a false treason case is not to detain foreign lawyers, but to drop the case altogether."

The Tanzania Human Rights Defenders Coalition said it was shocked by what it called the "arbitrary arrests", as Karua had been allowed into Tanzania to observe proceedings when Lissu appeared in court on 15 April.

Human rights groups have been increasingly concerned about a crackdown on the opposition in Tanzania ahead of presidential and parliamentary elections due in October.

Lissu cannot seek bail because he has been charged with treason, a crime for which the maximum sentence is death.

He survived an assassination attempt in 2017 after being shot 16 times.

The opposition leader was arrested in April after he held a rally under the slogan "No Reforms, No Election".

He is demanding sweeping changes, saying Tanzania's current laws do not allow for free and fair elections. The government denies the allegation.

Since his arrest, his Chadema party has been barred from contesting the October poll after it refused to comply with the electoral commission's requirement to sign a code of conduct.

The document requires parties and their supporters to "behave well" and to "maintain peace and harmony" during the elections.

Chadema sees the code of conduct as a ploy to contain the opposition and for state repression to continue.

The CCM party, which has governed Tanzania since 1977, is expected to retain power following the latest developments.

President Samia Suluhu Hassan is expected to be its presidential candidate.

She was widely praised for giving Tanzanians greater political freedom when she took office in 2021 following the death of the incumbent, John Magufuli.

Her critics say Tanzania is once again seeing the repression that characterised Magufuli's rule. The government denies the allegation.