Long-time Ugandan leader Yoweri Museveni was declared the winner of the presidential election, with more than 60 percent of the votes, but the main opposition party rejected the results as fraudulent.
Museveni's nearest rival, opposition leader Kizza Besigye of the Forum for Democratic Change party, got 35 percent, according to final results announced by the election commission.
Besigye himself was under house arrest as Museveni was declared the winner, with heavily armed police standing guard near his residence on the outskirts of the capital, Kampala.
Museveni's ruling party, the National Resistance Movement, urged "all candidates to respect the will of the people and the authority of the electoral commission and accept the result. We ask all Ugandans to remain calm and peaceful and not to engage in any public disruptions." The party released the statement shortly after the results were announced.
However Besigye's opposition party appealed to "all Ugandans and the international community to reject and condemn the fraud that has been committed and to expose it to the fullest extent possible. Clearly what we are witnessing in the choreographed announcements of the fraudulent results is part of a creeping political coup d'état."
The election on Thursday was marred by lengthy delays in the delivery of polling materials, some incidents of violence as well as a government shutdown of social media which is ongoing.
The election was marked by an "intimidating atmosphere, which was mainly created by state actors," said the European Union observer mission. Uganda's election commission lacks independence and transparency and does not have the trust of all the parties, EU mission leader Eduard Kukan told reporters Saturday. Opposition supporters were harassed by law enforcement officials in more than 20 districts, according to the EU's preliminary report.
Police on Friday surrounded the headquarters of the FDC opposition party as Besigye met with members and a helicopter fired tear gas at a crowd outside. Police then moved in and took away Besigye, a 59-year-old doctor. He was later taken to his house which was guarded by police who prevented access to journalists.
After Besigye's arrest on Friday, his supporters took to the streets. Riot police lobbed tear gas and stun grenades at them and fired warning shots from automatic rifles, then chased them through narrow alleys, arresting some.
Besigye's party is alleging massive vote rigging and accuses the government of deliberately stalling voting in opposition strongholds in Kampala and the neighboring Wakiso district.
U.S. Secretary of State John Kerry spoke by phone with Museveni "to underscore that Uganda's progress depends on adherence to democratic principles in the ongoing election process," the State Department said. Kerry urged Museveni to rein in the security forces.
The 71-year-old Museveni took power by force in 1986 and pulled Uganda out of years of chaos after a guerrilla war. He is a key U.S. ally on security matters, especially in Somalia. Critics fear he may want to rule for life and they accuse him of using security forces to intimidate the opposition.
Besigye was Museveni's personal physician during the bush war and served as deputy interior minister in his first Cabinet. He broke with the president in 1999, saying Museveni was no longer a democrat.