Some members of the coalition government say they will go to court to challenge the law.
Conflict in eastern DR Congo's has forced 400,000 people to flee their homes this year alone, the UN says.
The Lakurawa group has been accused of attacks on top government officials and kidnapping.
Bernadino Rafael denies claims he worked with criminal groups to kidnap and kill protesters.
A selection of the week's best photos from across the African continent and beyond.
"I was scared he had come to beat me or finish me off," a government critic tells the BBC about his ordeal.
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