KAMPALA, Uganda — The United States called for the release of Uganda’s opposition leader, Kizza Besigye, who has been under house arrest since Friday, before President Yoweri Museveni was declared the winner of a presidential election marred by widespread irregularities.

Museveni won last week’s vote with 60.75 percent of the vote, according to the electoral commission; Besigye had 35.37 percent.

“We call for his immediate release and the restoration of access to all social media sites,’’ the State Department said Saturday evening. “Delays in the delivery of voting materials, reports of pre-checked ballots and vote buying’’ and “excessive use of force by police’’ had undermined the vote, it said. “The Ugandan people deserved better.’’

Besigye was arrested Friday after the police stormed his party’s headquarters. He was there tallying votes, which his party said included wins at polling sites in Uganda’s north, Kampala, and other areas of the country.

The election ran smoothly around the countryside, according to electoral observers, but not in Kampala, the capital city where opposition parties get much of their support. Voting there started up to seven hours late because the ballot papers were not available.

Besigye rejected the electoral commission’s results.

New York Times