President Obama will send about 100 U.S. troops to Uganda and nearby countries to combat the Lord’s Resistance Army and kill or capture its leader, Joseph Kony, who has been charged with war crimes for a decades-long campaign against civilians in Central Africa.

In a letter to Congress on Friday, Obama outlined a strictly advisory role for U.S. forces, whom he said would engage in combat only in self-defense. The initial military contingent numbering about a dozen troops arrived in Uganda on Wednesday, and will grow to full strength in the coming weeks.

The decision follows more than a year of study within the White House on how to support the intent of a bill passed by Congress to help several Central African nations defeat a destabilizing guerrilla movement.

Human rights officials have urged Obama to deploy troops against the Lord’s Resistance Army, arguing that it would be a justified use of force to resolve a humanitarian crisis. The International Criminal Court indicted Kony and four other commanders in 2005 on charges of war crimes and crimes against humanity.

But the deployment comes as the Obama administration is withdrawing from the battlefields of Iraq and Afghanistan, where long wars have tested the patience of the American public and consumed resources the president has argued are needed at home. White House officials said that this troop deployment — the most substantial to an African conflict zone since Marines landed in Liberia in 2003 — is modest in number and in the scope.

“This is an advise and assist mission,” said Tommy Vietor, spokesman for the National Security Council. “It’s an indication of our support for the ongoing regional effort to confront this threat.”

The Lord’s Resistance Army has been operating in the border regions of northern Uganda, the Democratic Republic of the Congo and other Central African nations for more than two decades. Led by Kony, a former altar boy with a messiah complex, the army has been fighting to install what it says would be a Christian government in Uganda based on the Ten Commandments.

Although numbering only about 250 armed members, the movement is notorious for its civilian killings and kidnappings, particularly of children. The White House estimates that roughly 385,000 people have been displaced from villages in the region as a result of those tactics.

A smaller group of U.S. military advisers assisted a previous Ugandan-led offensive against the Lord’s Resistance Army in late 2008 and early 2009. That operation backfired, however, as Kony’s group escaped and his fighters responded by committing a string of massacres against civilians.

Fewer than two dozen U.S. personnel were involved in that operation, in which they provided intelligence and guidance to a force of Ugandan and Congolese troops that were hunting Kony’s group in a remote area in northeastern Congo. Kony’s fighters slipped away and rampaged through nearby Congolese villages, killing several hundred people, according to human rights groups.

United Nations and human rights officials criticized the combined Ugandan-Congolese force for bungling the operation and failing to protect civilians from Kony’s retribution. U.S. military officials defended their advisory role afterward, blaming Kony’s group for the atrocities.

Obama notified Congress of the deployment Friday as part of his legal obligation under the War Powers Act. He signed the Lord’s Resistance Army Disarmament and Northern Uganda Recovery Act last year, and White House officials have been studying how to support the measure since then.

In his letter to Congress, Obama wrote that the “combat-equipped U.S. forces” will help “regional forces that are working toward the removal of Joseph Kony from the battlefield.” That could mean killing or capturing the warlord.

Since 2008, the U.S. government has provided $40 million to Central African governments to be used against the LRA, as the movement is known.

The troop deployment comes with the consent of President Yoweri Museveni of Uganda, who has blamed a lack of special forces and intelligence capability for his nation’s inability to defeat the relatively small LRA.

In his letter, Obama stated that the first troops will be based in Uganda, a U.S. ally in the region. They are primarily Special Operations Forces, Pentagon officials said, although they declined to say which branches of the armed services they were drawn from or to provide details about the kinds of training they will provide.

The officials said the U.S. military trainers will eventually work side by side with Ugandan and other African forces in the region as they pursue the Lord’s Resistance Army, but will stop short of engaging in direct combat, unless it is in self-defense. Obama wrote that future U.S. forces also will deploy in South Sudan, the Central African Republic, and the Democratic Republic of the Congo.

In an essay published last year in Foreign Policy magazine, Kenneth Roth, executive director of Human Rights Watch, argued that deploying U.S. troops to help arrest Kony “would reaffirm that mass murder cannot be committed with impunity.”