United States has criticised the handling of Uganda’s disputed presidential election and raised concerns about the house arrest of an opposition leader who failed to end President Yoweri Museveni’s 30-year rule.

Museveni, one of Africa’s longest serving leaders and a U.S. ally, was declared winner on Saturday but opponents rejected the outcome of the election. European Union and Commonwealth observers have also criticised the handling of Thursday’s poll.

Main opposition candidate Kizza Besigye was arrested three times this week and alleges the police have put him under house arrest and blocked his electronic communication. Besigye has described the election as a sham and another challenger, Amama Mbabazi, said the poll was “fundamentally flawed”.

The U.S. State Department said it was concerned by Besigye’s continued house arrest and the shuttering of social media in Uganda, where Facebook, Twitter and WhatsApp have faced outages since election day.

“We call for his immediate release and the restoration of access to all social media sites,” Mark Toner, U.S. State Department deputy spokesperson, said late on Saturday.

He said the widespread reports of irregularities and the conduct of officials was “deeply inconsistent with international standards and expectations for any democratic process”.

Ugandan deputy government spokesman, Shaban Bantariza, dismissed the U.S. criticism, saying it “appears partisan and lacks merit”.

He added: “The few and isolated irregularities that occurred can not be used to discredit the integrity of an exercise that otherwise went smoothly.”