Tanzania's main opposition party has been barred from participating in this year's election, days after its leader was charged with treason.

Ramadhani Kailima, director of elections at the Independent National Elections Commission, said that Chadema had failed to sign a code of conduct document that was due on Saturday, meaning the party was disqualified from October's elections.

Last week, Chadema's leader Tundu Lissu was arrested and charged with treason following a rally in southern Tanzania at which he called for electoral reforms.

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

"Any party that did not sign the code of conduct will not participate in the general election," Mr Kailima said on Saturday, adding that Chadema would also be banned from taking part in any by-elections until 2030.

Earlier on Saturday, Chadema had said that it would not participate in a code of conduct signing ceremony, as part of its drive for voting reforms.

The country is due to vote in parliamentary and presidential elections, where Lissu was expected to challenge incumbent President Samia Suluhu Hassan.

When Hassan first came to power in 2021, after the death of her predecessor John Magufuli, she was praised for reversing some of his more authoritarian tendencies.

Campaigners and opposition parties have since accused Hassan's government of an intensifying crackdown on political opponents, citing arrests and abductions of opposition members. The government has denied the accusations and launched an investigation into the abductions.

One of the longest-reigning parties in Africa, CCM - or Chama Cha Mapinduzi - has governed Tanzania for over five decades.

Under the slogan "No Reforms, No Election", Lissu has argued that there was no possibility of free and fair elections without changes to how elections are run in Tanzania.

Lissu said that the make-up of the electoral commission needed to change and should not include people directly appointed by Hassan.

Authorities accuse Lissu of seeking to disrupt the election and incite a rebellion.

He has been remanded in custody and his treason case adjourned until 24 April. His lawyer, Rugemeleza Nshala, told Reuters that the charges were politically motivated, adding: "You cannot separate these charges from politics."

The opposition leader has been arrested on numerous occasions and in 2017 survived an assassination attempt in which his vehicle was shot 16 times.

He then went into exile, returning briefly in 2020 to run against Magufuli in that year's election. He left after the results were announced, complaining about supposed irregularities.

He then returned again in 2023, following changes introduced by Samia which her government said were aimed at allowing greater opposition freedom.