The police in Uganda have arrested a former prime minister who who was preparing to challenge President Yoweri Museveni in the 2016 elections, his lawyer said.

The lawyer, Fred Muwema, said Patrick Amama Mbabazi was held in Njeru, 80 kilometrast of Kampala on his way to address a rally.

“Mbabazi was arrested with his daughter and driver, but police say they carried out preventive arrests,’’ the lawyer said.

However, the police said that the rally Mbabazi was planning to address was illegal and that any member of the public trying to attend it would be breaking the law.

Reports said Mbabazi was later released on bail but could not be immediately confirmed.

The arrest took place while Museveni was in Juba to attend the Independence Day celebrations of South Sudan.

One of Africa’s longest-serving rulers, Museveni was expected to seek a new term in elections scheduled for February 2016.

Critics say he has prevented the opposition from campaigning in order to extend his 29-year rule.

Mbabazi was regarded one of Uganda’s most powerful men until Museveni sacked him from the post of prime minister in 2014 over his alleged presidential ambition.

Another opposition leader and presidential hopeful, Kizza Besigye, was also arrested near Kampala, a report said.