Kenyan President Uhuru Kenyatta on Saturday sent a message of congratulations to his Tanzanian counterpart John Pombe Magufuli following his re-election in the just concluded general election.
The 61-year-old was returned to power with 84 percent of votes in a poll his main rival branded a fraud.
Magufuli was declared victor of Wednesday's election with 12.51 million votes (84 percent) against 1.93 million (13 percent) for his main challenger, Tundu Lissu from leading opposition Chama Cha Demokrasia na Maendeleo.
Lissu has previously said that he will not accept the eventual election results.
The Tanzanian elections were marked by low voters turnout: the IEC counts certified around 50 percent of the electoral roll of 29 million voters casted their ballots.
The ruling Chama Cha Mapinduzi party won parliament seats in 253 of the 261 constituencies announced so far, achieving upsets in opposition strongholds by wide margins.
Magufuli's CCM party, a version of which has held power in Tanzania since independence from Britain in 1961, had already retained power in the semi-autonomous Indian Ocean archipelago of Zanzibar after its presidential candidate, Hussein Mwinyi, won with 76% of the vote.
Several groups including Tanzania Elections Watch (TEW) have poked holes in the election saying irregularities witnessed before and during the poll affected its credibility.
Lissu has rejected the vote while alleging "widespread irregularities" and called for peaceful demonstrations.
The opposition said 10 people were killed on Monday and Tuesday, and Hamad decried the election as a "military exercise" overshadowed by violence and cheating.
"The results should not be recognized by any country in the world, should not be recognized by the African Union and the Commonwealth", Lissu told Reuters. "It is not an election".
Most global media were unable to gain accreditation to cover voting on the mainland, and major social media networks were blocked, accessible only through virtual private networks (VPN).
"We are concerned by credible reports of election irregularities and the use of force against unarmed civilians, and will hold responsible individuals accountable", U.S. state department spokeswoman Morgan Ortagus said on Twitter.
In a statement, the USA ambassador to Tanzania Donald Wright urged relevant authorities to come together and address the concerns raised by different parties in the election.
Magufuli was first elected in 2015 on an anti-corruption ticket which endeared him to a population tired of scandals under his predecessor Jakaya Kikwete.
The feared "zombie" private militia of the ruling party swarmed the city, clad in black and with bandannas covering their faces.
"We knew it wouldn't be free and fair, but nobody expected this", she told AFP.