Police later continue with their operation to disperse Besigye’s supporters who engage them in running battles.
Kerry “expressed his concern about (Besigye’s detention) and harassment of opposition party members during voting and tallying, and he urged President Museveni to rein in the police and security forces”.
Mr Besigye’s supporters resisted the police, who took up positions outside the headquarters of the Forum for Democratic Change (FDC) party.
Besigye is considered Museveni’s main rival and was detained by police twice during the week before the election.
Early results showed Museveni, a Western ally against security threats including Islamist militants, with a sizeable lead of 62 percent based on a count of ballots in 42 percent of polling stations.
Following the election, Kizza Besigye, a “prominent” candidate for president, was arrested.
Tension has gripped parts of Kampala with fears that violence could erupt if Besiyge is not declared victor in the hotly contested polls.
Initial results are expected as early as Saturday afternoon with the leading presidential candidate requiring more than 50 percent of votes cast to avoid a run-off.
“The FDC must fall in line with the laws and wait for the Electoral Commission to announce results.” said Andrew Kaweso, head of police human resources.
When opposition supporters tried to resist, the police fired several canisters of tear gas behind the gates.
A police spokesperson said the cordoning off of the FDC headquarters was necessary. “But where it is not a free and fair election then we must fight for free and fair elections because that is the essence of our citizenship”. “The security forces must act with restraint”.
The voting Thursday suffered delays in delivery of voting materials, especially in areas seen as opposition strongholds, and was seen by the opposition as deliberate.
Museveni is attempted to be re-elected as president after 30 years in power.
Besigye was briefly arrested late on Thursday after visiting a house in Kampala where he suspected ballot-stuffing was taking place. A government official said social media was not available throughout Uganda for “security reasons”. “Museveni has overstretched the goodwill Ugandans gave him”.
Besigye, 59, was Museveni’s personal physician during a war and served as deputy interior minister in Museveni’s first Cabinet.
Museveni, one of Africa’s longest-serving leaders, has presided over strong economic growth, but faced mounting accusations at home and overseas of cracking down on dissent and failing to tackle corruption.