An African Union (AU) backed force has officially assumed command of operations against Uganda's notorious Lord's Resistance Army (LRA), officials said.

Major Alex Ahabyona, an intelligence officer for LRA leader Joseph Kony operation, said the ceremony to launch the move took place on Tuesday in the South Sudanese town of Nzara.

But officials say a scarcity of resources and unresolved disagreements over troop deployments still pose major impediments.

The AU force aims to co-ordinate soldiers already hunting LRA from Uganda, South Sudan, the Democratic Republic of Congo and Central African Republic.

In-depth coverage of campaign targeting Ugandan rebel

Led by Kony, a self-styled mystique leader, the LRA has been waging a brutal campaign of abductions, rapes and defilement in a lightly governed remote patch of jungle straddling the borders of the Central African Republic, the Democratic Republic of Congo and South Sudan since it was ejected from Northern Uganda in 2005.

The LRA's notoriety was cast in a global spotlight earlier this year after a controversial video highlighting its brutality became an instant internet sensation and was viewed by tens of millions of people.

At a command handover ceremony in Yambio, AU's special envoy on the LRA, Francisco Madeira, said the DRC had still not contributed troops but some commitments had been made and said the force required assistance to help it function properly.

"We need more support, I don't have to elaborate on these because my predecessor has done this so well. We need support in terms of means of transport, communication, medicine, combat rations and uniforms for the troops tracking the LRA. This is particularly important and critical and most urgent for the central African troops who handed over their contingent despite the challenges facing them," Madeira said.

In hiding

Although all the regional armies have been involved in fighting the LRA, it is the Ugandan army that has pursued him up to the Central African Republic, where he is currently believed to be hiding.

At the same ceremony, Uganda's defence minister, Chrispus Kiyonga, said there were still disagreements over areas of operation by troops from different countries.

"We are yet to fully agree on how this troops will operate because now they are going to be one force, a regional task force with its commander," Kiyonga said.

"There are two concepts: There are people who think that the SPLA [Sudan People Liberation Army] should only work on the side of Sudan, that the army of the Central African Republic should only work there [within its own borders] ... but there is the other concept that some of us support, [which is] that once there is one unified force, co-ordinated force then it should go wherever Kony is. We think that way, it will be more effective."

Kiyonga said the latest intelligence indicated LRA was now down to 200 guns and that the entire group was numbering about 500 people including women and children in rebel captivity.

Barack Obama, the US president, injected momentum in anti-LRA efforts last October when he sent 100 Special Forces to help provide intelligence and training support to the regional armies..