U.N. humanitarian officials estimate that tens of thousands of civilians have been displaced by the conflict in the eastern Democratic Republic of Congo.
Amnesty International, in a 66-page report, said the transfer of weapons into "abusive hands" in the country highlights the need for an arms trade treaty that would strengthen the United Nations' arms embargo system.
The organization said that members of the U.N. Security Council typically impose an arms embargo once weapons are in use by militants.
"As such a U.N. arms embargo is often imposed too late to prevent serious violations of international human rights and humanitarian law," the organization said.
Violence in DRC has intensified since rebel Gen. Bosco Ntaganda, wanted by the International Criminal Court for war crimes, waged mutiny in April.
Amnesty International said countries-- ranging from China, Ukraine and the United States -- have supplied weapons to the DRC military, which become a source of arms for militant groups in the country.
"Past and current violations of international human rights and humanitarian law committed by all parties to the conflict have been sustained by the easy availability of arms, including ammunition," the organization said.