US President Barack Obama said Friday he is sending 100 combat troops to central Africa to help and advise forces battling the Ugandan Lord's Resistance Army rebels accused of gross human rights abuses.

"These forces will act as advisers to partner forces that have the goal of removing from the battlefield Joseph Kony and other senior leadership of the LRA," Obama said, but warned they would not lead the fighting themselves.

The mostly special operations forces could deploy in Uganda, South Sudan, the Central African Republic and Democratic Republic of the Congo, subject to approval of regional governments, Obama said in a message to Congress.

LRA rebels are accused of terrorizing, murdering, raping and kidnapping thousands of people in the four nations, and tens of thousands of people died in their 20-year war with security forces in northern Uganda.

"Although the US forces are combat-equipped, they will only be providing information, advice and assistance to partner nation forces," the president said.

"They will not themselves engage LRA forces unless necessary for self-defense. All appropriate precautions have been taken to ensure the safety of US military personnel during their deployment."

A small group of troops deployed to Uganda on Wednesday and additional forces will deploy over the next month.

Pentagon officials said the troops would travel to regional capitals to work with government officials, military officers and peacekeeping missions.

"There is a clear end state -- to enable local forces to render the LRA ineffective," Pentagon spokesman George Little said, adding that US forces would offer training in tasks like tracking, intelligence assessment and conducting patrols.

He said that the required US forces to fulfill the long-standing request had not been available until now.

State Department spokeswoman Victoria Nuland said Washington has provided more than $40 million in logistical support, equipment and training to counter-LRA operations by armies in the region since 2008.

Heading a movement based on a mix of religion and brutality, Kony a self-styled mystic and religious prophet, claims to be fighting on divine orders to establish theocratic rule based on the Bible's 10 Commandments.

The civil war effectively ended in 2006 when a peace process was launched, but Kony and his top lieutenants, commanding forces including child soldiers, continue to commit atrocities.

General Carter Ham, head of US Africa Command, said last week his best estimate was that Kony was probably in the Central African Republic.

Helping central African nations in hunting down the LRA leadership was a "worthy goal" given the "unspeakable atrocities" committed against civilians, women and children, Republican Senator John McCain said.

But he recalled that previous humanitarian deployments in Lebanon and Somalia had resulted in tragic US losses and called on Obama to consult Congress about deployments, a step he said was not taken regarding the African mission.

Richard Downie, deputy director of the Africa Program at the Center for Strategic and International Studies, said the operation to hunt down LRA leaders would be "an incredibly difficult and complicated operation."

"They are experienced fighters divided into small groups and spread across an incredibly wide, ungoverned part of the world," he said.

Obama said in his message that the LRA had "murdered, raped, and kidnapped tens of thousands of men, women, and children in central Africa."

In 2009, Congress enacted a law expressing support for increased US efforts to mitigate and eliminate the threat posed to civilians by the LRA.

And a year ago, Obama unveiled a plan to disarm the LRA and increase humanitarian access to affected communities.

Human rights and anti-genocide groups welcomed Obama's decision.

"President Obama is showing decisive leadership to help regional governments finally bring an end to the LRA's mass atrocities," said Paul Ronan, director of advocacy at Resolve.

John Prendergast, co-founder of the Enough Project, said the US troops could play a catalytic role if they were used as part of a wider multinational strategy.

"Missing elements include more capable forces dedicated to the apprehension of Joseph Kony and protection of civilians, and an intelligence and logistics surge from the US to help those forces succeed," he said.