Uganda's failed presidential challenger Amama Mbabazi launched a petition Tuesday challenging the win by President Yoweri Museveni last month, citing voter bribery and arrests.

But Museveni's closest rival, opposition chief Kizza Besigye, arrested multiple times during the election, was blocked from making a similar petition, his party chief said.

"Despite the challenges, massive arrests of our supporters, harassment and intimidation, we have today finally lodged our petition challenging the results of the just concluded elections," Mbabazi's lawyer Severino Twinobusingye told AFP Tuesday.

"We have been assured by the court that they will handle the petition expeditiously"

Museveni swept to his fifth election victory last month with 61 per cent of the vote.

Observers said the cards were heavily stacked against his opponents, as the 71-year-old's grip on his party and country — and his access to state resources — meant the result was never in any doubt.

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The petition was lodged at Uganda's Supreme Court in the capital Kampala.

"Our petition touches on a number of issues ranging from late delivery of ballots to arrests and intimidation of our candidate and supporters plus outright voter bribery," Twinobusingye added.

But Besigye could not deliver his petition due to "hostile actions by government", according to his Forum for Democratic Change (FDC) party president Mugisha Muntu.

"Because of hostility we have been subjected to by the government, the arrests of our candidate which came to nine times since the February 18 elections," Muntu said. "It's difficult for us to deliver our petition to court as mandated under the 10-day deadline."

In the days since the vote, armed police and soldiers have maintained an aggressive, highly visible presence on the capital's streets to keep a lid on things, while Besigye has been prevented from leaving his home by a succession of mob-handed arrests.

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"We are coming out with the next course of action in next few hours," Muntu said.

"In last 24 hours there has been arrest of our supporters, and even journalists arrested during the live coverage of the police siege of Dr Besigye - its been a challenging moment for us and Ugandans."

Seven journalists were arrested by police on Monday, the Daily Monitor reported, while the Committee to Protect Journalists on Tuesday condemned an "extended series of attacks on journalists covering the political opposition."

After Besigye, Museveni's next closest challenger was former prime minister Mbabazi, a former ruling party stalwart who trailed in distant third. He won less than two per cent.