Leading Kenyan lawyer and the country's former Justice Minister Martha Karua says she has been detained in Tanzania after flying in for the court appearance of opposition leader Tundu Lissu.

Karua said in a social media post that she had been detained at the main international airport and was awaiting deportation, along with two colleagues who had flown in with her. Tanzanian authorities have not yet commented.

Tanzanian politician Lissu 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.