A military force set up by the African Union to hunt down fugitive Ugandan warlord Joseph Kony is being launched in South Sudan.
The AU says the 5,000-strong force will exist for as long as it takes to capture or kill Mr Kony.
His Lord's Resistance Army (LRA) is accused of rape, mutilation, murder and the recruitment of child soldiers.
Regional UN envoy Abou Moussa said Mr Kony was believed to be in the Central African Republic.
He said the LRA had dwindled in size but was still creating havoc.
Mr Kony and his close aides have been wanted by the International Criminal Court (ICC) in The Hague since 2005.
The AU mission comes in the wake of a huge Internet campaign targeting the LRA leader. The video - Kony2012 - has been viewed more than 100 million times on YouTube.
"We need to stop Kony with hardware - with military hardware in this case," said Francisco Madeira, the AU's special envoy on the LRA.
"We are on a mission to stop him."
Mr Moussa, speaking in Entebbe, Uganda, where African ministers agreed the new strategy, said the LRA was believed to have dwindled to between 200 and 700 followers but remained a threat.
"We do have information that he may be in the Central African Republic," he said.
"The most important thing is that no matter how little the LRA may be, it still constitutes a danger... they continue to attack and create havoc."
Mr Moussa said that soaring international interest in Mr Kony had been "useful, very important".
The AU force will have a Ugandan commander and comprise troops from Uganda, South Sudan, Central African Republic and Congo - all countries in which the LRA has operated.
It is based in Yambio, in the west of South Sudan, near the border with the Central African Republic and the Democratic Republic of Congo.
Tne BBC's James Copnall in Khartoum says the new force faces a difficult task over a vast area.
There have been calls for the US - which already has military advisers in the region - to supply planes and satellite technology to help track the LRA.
Uganda already has troops in the jungles of the Central African Republic.
The LRA's campaign of terror began in northern Uganda more than 20 years ago when it said it was fighting for a Biblical state and the rights of the northern Ugandan Acholi people.
The LRA is listed by the US as a terrorist organisation and now operates mainly in neighbouring countries.
Mr Kony refused to sign a peace deal with the Ugandan government in 2008 when it could not guarantee the withdrawal of the ICC arrest warrants.
The half-hour video, Kony2012, was made by US campaigners Invisible Children.
However, critics, have questioned the methods of the non-profit group, accusing it of spending most of its raised funds on salaries, travel expenses and film-making.