The chief prosecutor for the International Criminal Court announced this week he was seeking to add war crimes and crimes against humanity charges to the arrest warrant for rebel Congolese Gen. Bosco Ntaganda.
HRW said he recruited at least 140 boys and young men into his forces since he rebelled in mid-April. Of those, 17 were under the age of 15 and seven of the 149 recruits died in fighting in the Democratic Republic of Congo.
Anneke Van Woudenberg, a senior researcher in African affairs at HRW, said the latest trend confirms ICC claims of crimes related to child soldiers.
"Children and civilians in eastern Congo will remain at grave risk so long as Ntaganda is at large," the researcher said in a statement.
Violence was reported recently in DRC as a government deadline for militant surrender approaches. U.N. officials had said an estimated 40,000 civilians were displaced by conflict since April.
The United Nations said restoring the government's authority and establishing a professional security force are required for peace.