Tanzania's opposition on Saturday called on supporters to take to the streets to protest President John Magufuli's landslide election victory, which it says was fraudulent, demanding a fresh vote.
Magufuli was declared the winner Friday with a crushing 84 percent of votes, while his Chama Cha Mapinduzi (CCM) ruling party took 97 percent of the 264 elected parliament seats.
The country's two main opposition groups, Chadema of defeated presidential candidate Tundu Lissu, and ACT-Wazalendo, held a joint press conference in Dar es Salaam in which they denounced the election and called their supporters to action.
"Firstly, we call for fresh elections as soon as possible. Whatever happened is not an election," Chadema chairman Freeman Mbowe said.
"We call for continuous, peaceful, countrywide demonstrations until our demands are met," he said, adding these would begin on Monday.
ACT-Wazalendo leader Zitto Kabwe said the decision was for "the future of our country".
"We cannot accept going back to a one-party system. God willing we will win in this war."
Democracy was introduced in 1994 and Tanzania has been seen as a haven of stability in a volatile neighbourhood but critics have raised alarm over a slide into autocracy under Magufuli.
The 61-year-old, nicknamed "The Bulldozer", was in his first term accused of flouting due process and brooking no criticism.
His main opponent this time around, Lissu, won only 13 percent of the vote, after denouncing widespread fraud and intimidation of the opposition during the election and following years of repression and jailing of government opponents.
Lissu, who returned to Tanzania in July after three years abroad recovering from 16 bullet wounds sustained in an assassination attempt, said his party's agents had been kicked out of polling stations and that there had been ballot box stuffing.
In 2015, Magufuli won with 58 percent of the vote.
The outcome of Wednesday's vote will further cement the power of a party that has been in power since independence in 1961.
The opposition parties again asked the international community not to recognise the result.
The result of presidential elections cannot be contested in Tanzania although the parliamentary outcome can be challenged.
"The door is closed for us to challenge the presidential results in court, and that is why we have decided to take this to the people, who have the power," Lissu said at the press conference.
Magufuli received congratulations from his counterparts in Burundi -- also regularly accused of crushing the opposition -- and Uganda -- where President Yoweri Museveni is seeking a sixth term next year.
Credible reports of irregularities
The election took place with little monitoring from foreign observers and most international media were unable to gain accreditation to cover voting on the mainland.
"We are concerned by credible reports of election irregularities and the use of force against unarmed civilians, and will hold responsible individuals accountable," US state department spokeswoman Morgan Ortagus said on Twitter.
"We urge Tanzanian authorities to take immediate steps to restore faith in the democratic process."
In Zanzibar, a semi-autonomous territory that elects its own leader and lawmakers, as well as the Tanzanian president, a call to protest against the results saw key opposition figures arrested and beaten.
Authorities there deployed thousands of soldiers, police and a feared private militia known as "zombies", who were seen beating and rounding up civilians, crushing any potential demonstrations before they started.
Just four of the 50 parliamentary seats up for grabs on Zanzibar went to ACT-Wazalendo.
The CCM presidential candidate Hussein Ali Mwinyi was declared the victor.
Mbowe said Saturday that 20 people had died across Tanzania in election-related violence. The opposition in Zanzibar said Friday that 13 people had been killed on the islands alone.
Police had earlier denied the deaths on Zanzibar, which could not be independently confirmed.