Dar es Salaam (AFP) - Former Tanzanian prime minister Edward Lowassa on Tuesday defected from the ruling Chama Cha Mapinduzi (CCM) party, accusing it of "oppressive leadership", less than three months ahead of a general election scheduled for October 25.
Lowassa, 61, was the east African country's prime minister between 2005 and 2008.
He said he was now joining the opposition Chadema party.
"CCM leaders have of late turned to be undemocratic, oppressive and witch-hunting. I am no longer with them," Lowassa said, adding he had switched to Chadema "to bring positive and meaningful change in our society."
Lowassa had joined the race earlier this month to run as the CCM's presidential candidate, where he was seen as a frontrunner among 42 candidates, but lost out to government minister John Magufuli.
Following his defeat, Lowassa claimed the ruling party was "infested with leaders who are dictators, undemocratic and surrounded with greedy power mongers."
The ruling CCM party has dominated politics since modern Tanzania was formed in 1964, and currently has two-thirds of seats in parliament.
Tanzania, with over 50 million people, is east Africa's most populous country, with economic growth of more than seven percent, according to the World Bank.
Despite advances, the country remains very poor by regional and international standards, the World Bank says, with agriculture the key sector, providing a quarter of gross domestic product and employing three-quarters of the population.
The government has also been criticised for failing to stamp out rampant corruption.