Electoral authorities in Tanzania on Saturday called on police to investigate fears that some political parties were preparing to train militia groups ahead of next month's national elections.
The concern has emerged as campaigning heats up prior to the October 25 polls, in which the long-time ruling Chama Cha Mapinduzi (CCM) party's candidate John Magufuli is hoping to succeed President Jakaya Kikwete.
But Magufuli, 55, is facing what is seen as the tightest electoral race in the east African nation's history, with the main opposition parties uniting around ex-prime minister Edward Lowassa, 61, who recently defected from the CCM.
"The Commission has received information that certain political parties were preparing to give military training to more than 1,500 youth in order to cause trouble during the elections," Damian Lubuva, the National Election Commission's president, said in a statement.
"Even if this information only comes from one camp, the Commission requests the police to investigate and take the necessary action," it added, without naming any particular party.
"No party is allowed to use such a militia. It is against the law."
The statement also came after one person was killed earlier this month in a clash between CCM supporters and the main opposition Chadema party.
The ruling CCM party has dominated politics since modern Tanzania was formed in 1964, and currently has two-thirds of seats in parliament.
But it has been weakened by internal splits and a string of graft scandals, and recently suffered defections of high-profile members -- including ex-prime minister Frederick Sumaye and former home affairs minister Lawrence Masha -- to the opposition coalition.
Tanzania is one of the region's most stable countries, and Kikwete is also standing down at the end of his second and final mandate -- in contrast to President Pierre Nkurunziza in neighbouring Burundi whose bid to stay in office sparked weeks of violence and a coup attempt.
Another neighbour, Kenya, was also hit by post-election tribal violence in 2007-2008 which left more than 1,000 dead.
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.