Tanzania's opposition presidential candidate Edward Lowassa on Wednesday called for a recount of Sunday's poll, citing voting irregularities in the East African nation's tightest elections in more than five decades.
Earlier in the day, the election in Tanzania's semi-autonomous Zanzibar archipelago was annulled after the local election commission cited "gross violations", raising tension on the islands that have been a hotbed of opposition to the ruling Chama Cha Mapinduzi (CCM) party.
Tanzania's National Electoral Commission (NEC) had planned to reveal the winner of the presidential race on Thursday, but Lowassa called on NEC to cancel that announcement.
"We demand that NEC should do a verification of the results and recount the votes," Lowassa said at a news conference in Tanzania's commercial capital, Dar es Salaam.
The electoral commission and the ruling CCM party, in power since British colonial rule ended in 1961, have both dismissed opposition allegations of rigging.
"Claims of vote rigging highly misleading ... it is not true at all," the chairman of the National Electoral Commission, Damian Lubuva,told journalists on Wednesday.
Results from the presidential race began trickling in on Monday, showing the CCM candidate, John Magufuli, leading the former prime minister Lowassa.
On Zanzibar, an official from the opposition Civic United Front (CUF) said annulling the poll was a ploy to rerun the vote it had won. There was no immediate comment from CCM, but it has previously said it was on track for a slim win there.
The Zanzibar vote was part of a national election to pick a new president and parliament in the east African country. Lowassa did not demand a recount of the parliamentary vote.
CCM said it had complaints about violations in at least four parliamentary constituencies where it had lost to the opposition and would to go court to contest the parliamentary outcome. But it said the overall picture was that "elections were free and fair" and that voting reflected the will of people.
Tanzania has been one of the continent's most politically stable nations but Zanzibar has often been a kernel of political tension due to its traditional opposition to central government.
This election has been the most hotly contested in CCM's history after the main opposition parties formed a coalition for the first time, fielding a single presidential candidate for Zanzibar and a single candidate for the united republic.
"There is a need to hold fresh elections," Zanzibar Election Commission Chairman Jecha Salim Jecha said in a statement, citing "gross violations".
Lubava said the annulment in Zanzibar would not affect the Tanzania vote and the process would continue as planned.
On Monday, police fired teargas to disperse CUF supporters in Zanzibar after they gathered to celebrate what the opposition party said was its victory. The CCM had disputed this.
"It’s an attempt to try and disrupt the process and my feeling is that they just want to create chaos," CUF spokesman Ismail Jussa told Reuters after the commission's announcement.
There was no immediate comment from CCM officials.
The CUF in Zanzibar and Chadema on the mainland are part of the broader Ukawa opposition coalition.