Former Prime Minister Amama Mbabazi and Kizza Besigye (pictured above) were taken into police custody on Thursday, Ugandan government-owned newspaper New Vision reported.

Mbabazi was arrested in central Uganda as a "preventive" measure by the police.

"I am telling you… I am the police and I have arrested him. He has to stick to what the law requires… He's now under incarceration," Assistant Inspector General Andrew Felix told reporters.

Kizza Besigye was detained near his house on the outskirts of Kampala.

"He had just left his home this morning going to [sic] the American Embassy for a meeting with the ambassador when police intercepted him and ordered him to either return home or be arrested… He refused to return home and was immediately arrested," Francis Mwijukye, Besigye's aid told Reuters news agency.

Both leaders were believed to have been planning campaign rallies for presidential elections, due to take place next year and could pose a challenge for President Yoweri Museveni, who has led his country for nearly three decades. He has the support of the ruling National Resistance Movement (NRM) for next year's elections.

Mbabazi, a former ally of Museveni, announced last month that he would stand against the current president in the 2016 elections. The announcement sparked criticism from the government, which said many setbacks in its term happened when Mbabazi was the NRM's secretary-general.

Besigye, a former doctor who personally attended to Museveni, has challenged the president three times already. He lost the 2011 elections and consequently led anti-government protests, during which he was arrested several times.

mg/jil (AFP, AP, Reuters)