Ugandan police arrested opposition leader Kizza Besigye on Monday for the second time in a month, his party said, as he was leaving his house to join a protest against soaring food and fuel prices.
Ann Mugisha, deputy foreign envoy for the Forum for Democratic Change, said his exact place of detention was unclear after being moved from different police stations.
"Besigye ... was taken in a police vehicle and his driver chased them but he lost them as they entered a police barracks. Up to now we don't know where he is and we're calling it an abduction," she told Reuters.
Ugandan police officials were not immediately available for comment. Last week they said Besigye would be kept under house arrest until he promises to stop participating in anti-government protests, a move a court ruled as illegal.
The authorities had briefly detained Besigye, a one-time presidential contender, earlier this month when he joined a 'walk-to-work' protest on the outskirts of the capital, Kampala.
Deadly protests in April and May over high food and fuel prices were crushed by President Yoweri Museveni, who has been in power for more than two decades and who blames the high costs on outside pressures.
Besigye was badly beaten and put under house arrest at the time and has since stayed away from most major protests that the opposition has tried to launch.