Uganda's former Prime Minister Amama Mbabazi has told the BBC he "will not back down" in his preparations for a presidential bid, despite his arrest on Thursday.
Mr Mbabazi, a former close ally of President Yoweri Museveni, was arrested while travelling to canvass support.
The government says that he violated public order laws by attempting to hold meetings without permission.
The long-serving president is widely expected to seek re-election next year.
Leading opposition figure Kizza Besigye was also arrested on Thursday ahead of a planned campaign rally outside the capital Kampala.
Both men were later released without charge.
Mr Mbabazi said he held President Museveni directly responsible for his arrest.
He told the BBC's Newsday programme that the only other time he had been arrested was in 1976, under the rule of Idi Amin.
"Even Idi Amin did not arrest my children," he said, referring to the arrest of his daughter Rachael, who had been travelling in the same convoy as him when police blocked the route and detained them.
Last month, Mr Mbabazi said he would challenge Mr Museveni, 70, by seeking the nomination of the ruling National Resistance Movement (NRM).
Uganda's Information Minister Jim Muhwezi rejected his criticism of the government, telling Newsday that Mr Mbabazi "was arrested because he disobeyed lawful orders and disobeyed police".
Mr Museveni has been in power in Uganda since 1986, and his critics say he has become increasingly repressive.
However, his supporters say he has provided stability and has improved the living standards of Ugandans.