President Yoweri Museveni has begun the formalities needed to run for reelection in Uganda's 2016 elections, his spokesman said on Wednesday, a move that could see him extend his rule to 35 years.

Don Wanyama, Museveni's spokesman, said the veteran leader has paid 20 million shillings ($6,025) in fees to file for nomination as the presidential candidate of his ruling National Resistance Movement's (NRM).

The east African country is set to hold its presidential and parliamentary elections between February and March next year.

In the past three elections, NRM officials have not allowed any internal rival to run for the nomination against Museveni.

In the presidential poll, analyses say Museveni, 70, should face a strong challenge from former ally Amama Mbabazi and popular opposition leader Kizza Besigye, but ultimately win.

"The president has paid nomination fees," Wanyama said.

Museveni, Wanyama added, had paid the money through his agents and he was expected to personally come and pick up the nomination forms according to the party's internal rules.

Critics have accused security forces of harassing Museveni's opponents after police last week arrested Besigye and Mbabazi shortly before they launched their own campaigns to promote their candidacy.

Police accused them of not complying with electoral and public order management laws. They were released after spending about 12 hours behind bars.

Mbabazi, who is also seeking the NRM nomination, was sacked as prime minister late last year amid suspicions he intended to seek the presidency. He is widely seen as retaining significant clout within the ruling party.

($1 = 3,319.6700 Ugandan shillings)