* Besigye's aide denies accusations
* Arrest seen as move to silence dissent against president
* Arrest follows media crackdown
By Elias Biryabarema
KAMPALA, June 20 (Reuters) - Ugandan opposition leader Kizza Besigye was arrested on Thursday for holding an unsanctioned rally and seeking to incite violence, police said, the latest move in what critics say is a campaign to silence dissent against the president.
The police detained Besigye, a former ally of President Yoweri Museveni, saying he was inciting a crowd that rallied to support Erias Lukwago, an opposition colleague and mayor of the capital Kampala who is facing a tribunal over charges that include abuse of office.
"We were surprised to see Besigye appear there. Then he started addressing and inciting people as usual, yet he had no police permission to do that," deputy police spokesman Patrick Onyango said, adding police used teargas to disperse the crowd.
Besigye would be charged if there was enough evidence that he had incited violence, Onyango said.
Francis Mwigukye, Besigye's aide who was with him when he was detained, dismissed the accusations. He said Besigye was on regular business in Kampala when an impromptu crowd gathered around his car and became angry when the police stepped in.
Rights lawyers say police often use a law that requires they be informed about rallies to clamp down on basic rights of association and freedom of speech. Police deny the charge.
Besigye, who has long led opposition to Uganda's leader, has lost three presidential elections to Museveni, saying the results were rigged, and has often been detained by police.
Opponents have increasingly criticised Museveni for what they describe as his autocratic style of rule. Journalists protested in May against a crackdown on the media that followed a rare public debate over who would succeed him.
Last month, the authorities halted operations at two newspapers and two radio stations after they reported a purported plot to assassinate people who said that Museveni was grooming his son, Muhoozi Kainerugaba, for power.
Speculation is growing that Museveni, one of Africa's longest-serving leaders, is lining up his son to take power at the end of his term in 2016, a move that would probably test the loyalties of Uganda's ruling elite. (Writing by Edmund Blair; Editing by James Macharia and Elizabeth Piper)