Ugandan police arrested opposition presidential aspirant Kizza Besigye on Wednesday as he prepared to travel to the country's eastern region for a rally, a move seen as escalating a crackdown on incumbent leader, Yoweri Museveni's opponents.
Besigye has often been targeted in the past by police, who have arrested him and banned his supporters from gathering in what officials term "illegal" rallies.
But rights activists and government critics say intimidation and harassment of opposition supporters and leaders is growing as presidential polls due between February and March 2016 near.
Museveni, 71 has led Uganda since 1986 and is seeking another five-year.
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Analysts say disillusionment is growing in his ruling National Resistance Movement party because of rampant corruption, a breakdown of essential public services and widespread violations of rights.
An unidentified police officer was shown on local television telling Besigye outside his residence in the outskirts of the capital Kampala that he was being placed under "preventive arrest."
"We have information that you're going out to engage in activities that may endanger property of the people. We are going to arrest you to prevent that," the policeman told Besigye as he sat in his vehicle.
Shortly after Besigye was put in a police truck and driven to a police post in Mukono, about 25 km east of Kampala where he was detained alongside Ssemujju Ibrahim Nganda, a legislator who is also spokesman for the main opposition party Forum for Democratic Change.
The party has picked Besigye as its flag bearer in the election.
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Moses Byamugisha, Besigye's lawyer, told Reuters police in riot gear had deployed around Besigye's residence from late Wednesday evening and placed roadblocks - some using metal spikes - on nearby roads.
Byamugisha said Besigye and other party officials had planned to travel to the eastern Ugandan towns of Jinja and Iganga to open offices there and hold rallies.
Police spokesman Patrick Onyango told Reuters the rallies are illegal as the Electoral Commission was yet to clear his candidacy.
Electoral officials and the police say the country's electoral law only allows candidates to formally campaign once the electoral body clears them.
Besigye and former prime minister Amama Mbabazi - another Museveni challenger - have variously accused police of intimidating and harassing their supporters, often breaking up their rallies with live rounds, teargas and water cannon.
Criticism of police brutality has intensified since Saturday when a video aired on local television showed police undressing a woman opposition supporter.
The incident happened when police blocked a convoy of opposition leaders including Besigye from travelling to the western Ugandan town of Rukungiri for a rally.
Photographs run in local newspapers and on social media also showed vehicles in the leaders' convoy with shattered windows and windscreens.