A senior official of Tanzania's main opposition party has been arrested amid a crackdown on dissenting voices ahead of next week's general election.

John Heche, deputy chairperson of Chadema, was detained while attempting to attend the treason trial of party leader Tundu Lissu.

In a statement, Chadema alleged that the government planned to "arrest senior party leaders and detain them until after the elections", which will take place on 29 October.

The government has not responded to this accusation.

Chadema said Heche was apprehended as he arrived at the High Court in Dar es Salaam on Wednesday.

The party also alleged that Heche is being transported to Tarime, a northern town more than 1,300km (820 miles) away from Dar es Salaam.

The police have not commented on the arrest, which was Heche's second detention in a week.

On Saturday he was briefly held as he attempted to cross into neighbouring Kenya, reportedly to attend the burial of former Kenyan Prime Minister Raila Odinga.

Tanzania's immigration department said in a statement that Heche had attempted to illegally cross the border, but Chadema dismissed this allegation.

Heche's arrest comes amid an outcry over the disappearance of a former Tanzanian ambassador, who was also a critic of the government.

Humphrey Polepole's family said he was abducted at his home in Dar es Salaam on 6 October. Polepole's brother said he had found the door to the house broken and a large amount of blood spilled.

President Samia Suluhu Hassan is running for a second term but this is the first time she has contested a presidential election as she took office in 2021 following the death of John Magufuli.

Representing the CCM party, she was initially praised for giving Tanzanians greater political freedom. However, she has since faced widespread criticism for increasing repression, including a crackdown on political parties and civil society.

Chadema has been banned from participating in next week's polls, and its leader Tundu Lissu has been detained since April.

Luhaga Mpina, the candidate of the second biggest opposition party ACT-Wazalendo has also been disqualified, leaving only candidates from minor parties to face President Samia.