The African Union (AU), backed by the United States, has put together a 5,000-strong military force to hunt down fugitive warlord Joseph Kony, whose profile has shot up following a celebrity-backed campaign against him.
Kony, accused of terrorising northern Uganda for two decades, is wanted by the International Criminal court for war crimes. He is accused of leading a group that abducted children to use as fighters and sex slaves and hacked off living victims' limbs as a method of intimidation and revenge.
A video about Kony posted on YouTube by a California film-maker has been viewed by tens of millions of people, promoted on Twitter with the hashtag #Kony2012 and endorsed by major Hollywood celebrities.
The AU force aims to coordinate soldiers already hunting for Kony from South Sudan, the Democratic Republic of Congo (DRC), Central African Republic (CAR) and Uganda with logistical and intelligence help from Washington.
In October, US President Barack Obama said he was sending 100 military advisers to the four countries involved in the new AU force..
"The Americans are playing a pivotal role in some aspects," AU special envoy Francisco Madeira said on Saturday.
"They support us militarily, they support us with equipment, they support us with military advice, they support us even with intelligence and training," he told reporters at its launch ceremony in the South Sudanese capital Juba.
He gave no details on the troops' strategy. The force will be headquartered in Yambio in South Sudan near the border to the DRC.