* Museveni wins sixth term
* Opposition candidate Bobi Wine alleges fraud
* Election campaign marked by deadly crackdowns
* US diplomat criticises election as flawed
Ugandan President Yoweri Museveni has scored a decisive election victory to win a sixth term, the country's election commission said on Saturday, but his main rival Bobi Wine denounced the results as fraudulent and urged citizens to reject them.
The 76-year-old Museveni, in power since 1986 and one of Africa's longest-serving leaders, won 5.85 million votes, or 58.6% in Thursday's election. Wine had 3.48 million votes (34.8%), the Electoral Commission said in announcing the final results.
The campaign was marked by a deadly crackdown by security forces on Wine, other opposition candidates and their supporters. In the run-up to the vote local civil society groups and foreign governments questioned its credibility and transparency, after scores of requests for accreditation to monitor the election were denied.
The United States and an African election monitoring group complained of election irregularities and Wine, a 38-year-old singer-turned-lawmaker who had rallied young Ugandans behind his call for political change, called the results a "complete fraud".
"It’s an election that was taken over by the military and the police," he said in a phone interview from inside his home in the capital, Kampala, which was surrounded by soldiers who he said had forbidden him from leaving.
"It further exposes how dictatorial the Museveni regime is," added Wine, who campaigned to end what he called widespread corruption. "It's a mockery of democracy."
Army deputy spokesman Deo Akiiki told Reuters that security officers at Wine's house were assessing threats he could face: "So they might be preventing him in the interest of his own safety."
Museveni argued in the campaign that his long experience makes him a good leader and promised to keep delivering stability and progress. By 7 p.m. (1600 GMT), four hours after results were announced, the president had not issued a statement.
The government ordered the internet shut off the day before the vote and has not yet restored it.
After the results were announced, many neighbourhoods in normally bustling Kampala were unusually quiet as nightfall approached. Soldiers and police who had patrolled throughout the day remained on the streets in large numbers, witnesses said.
"These gunmen are all over and they are ready to kill," said Innocent Mutambi, 26, a welder. "I am sure what they announced is false, but right now we can't take them on, they will kill us."
Hundreds of the president's supporters rode motorcycles from the election tallying centre to downtown, where people danced with posters bearing the president's face.
Wine, whose real name is Robert Kyagulanyi, has said he has video proof of voting fraud that he will share once internet connections are restored.
He told Reuters on Saturday that his campaign has evidence that the military forced people at gunpoint to vote for Museveni and engaged in ballot stuffing and other rigging.
The electoral commission said on Friday that under Ugandan law, the burden of proof rested with Wine.
Reuters has not independently verified Wine's claims.
The Africa Elections Watch coalition, which deployed 2,000 observers in 146 districts, said in a statement that they had observed irregularities, including the late opening of most polling stations, missing ballot papers, and illegally opened ballot boxes.
The African Union also sent an observer mission but had no comment yet on the vote.
The US State Department’s top diplomat for Africa, Tibor Nagy, said in a tweet on Saturday that the "electoral process has been fundamentally flawed". He cited fraud reports, denial of accreditation to observers, violence and harassment of opposition members, and the arrest of civil society activists.
In addition to shutting off the internet, the government on Tuesday banned all social media and messaging apps. Wine and his supporters often used Facebook to relay live coverage of his campaign.
In the parliamentary election, where candidates were vying for 529 seats, at least 18 ministers from the ruling party lost their seats, Ugandan media reported. The country's vice president, Edward Ssekandi, also lost his race.
With results still coming in, local media reported that 56 candidates from Wine's National Unity Platform (NUP) had won their races.