A prominent Tanzanian activist has been released after being "kidnapped" on Sunday by three armed men on the streets of Kenya's capital Nairobi, her husband said, accusing Tanzania's national intelligence service of responsibility.

Maria Sarungi Tsehai, a human rights defender critical of Tanzanian President Samia Suluhu Hassan, was kidnapped by three armed men and taken into a black car in the Kilimani neighbourhood on Sunday afternoon, Amnesty International said.

"I am now safe, many thanks to everyone," Sarungi Tsehai wrote on X several hours later.

Her brief detention comes as the governments of both Tanzania and Kenya stand accused of abducting critics.

Sarungi Tsehai's husband David Tsehai said the couple sought refuge in Nairobi four years ago after fleeing Tanzania.

"It was the scariest moment of my life," he said in a video clip shared by the Law Society of Kenya late on Sunday.

"There is no doubt in my mind (it is) the thugs of the Tanzania Information and Security Services (TISS) who are behind this."

Spokespersons for Tanzania's government and TISS did not immediately respond to Reuters' request for comment. Kenya's police spokesperson also did not respond to a request for comment.

President Hassan ordered an investigation into the abductions last year, when several government critics were abducted and injured or killed by unknown people, in a pattern by which, rights groups say, the government targets opponents in the run-up to national elections expected later this year.

Amnesty International researcher Roland Ebole said Sarungi Tsehai's abduction was another example of "transnational repression that is happening on Kenyan soil," accusations Kenyan authorities deny.

In November a Ugandan opposition figure was kidnapped in Nairobi and forcibly repatriated to Kampala where he faces charges in a military court.