US special forces have set up a base in the Central African Republic as part of their regional hunt for fighters from the Ugandan-born Lord's Resistance Army group, military sources said Monday.

"The deployment of this contingent, the size of which is unknown, was carried out very discreetly with Ugandan military aircraft," a Central African military official said on condition of anonymity.

The US elite troops set up a base in Obo and are expected to coordinate their efforts with local government forces and Ugandan soldiers.

US President Barack Obama in October announced he was sending 100 special forces soldiers to Kampala to help Uganda track down LRA chief and international fugitive Joseph Kony, who has wreaked havoc over four nations for more than two decades.

Besides Obo, the US forces also have a forward base in South Sudan. They began deploying in Uganda earlier this month.

The rebels currently number several hundred, a fraction of their strength at their peak but still include a core of hardened fighters infamous for mutilating civilians and abducting children for soldiers and sex-slaves.

The majority of US troops will be based in Uganda while a smaller number will be based in jungle areas in neighbouring countries to advise regional armies tracking the rebels, US officials say.

Tens of thousands of people have been killed since Kony took up arms in the late 1980s, initially against the Ugandan government.

The International Criminal Court has a warrant against Kony, one of the continent's most wanted men.

Driven out of Uganda, the guerrillas have since scattered across a vast region of the Central African Republic, Democratic Republic of Congo and South Sudan, recruiting fighters from those nations over the years.

The LRA emerged from the frustrations of Uganda's marginalised Acholi ethnic group against the government, but its leaders have since dropped their national political agenda for the narrow objective of pillage and plunder.