Rebel groups in the Democratic Republic of Congo are using arms from many countries despite a strict UN arms embargo, according to a report.
The flow of munitions into eastern DR Congo has not stopped
Bullets from the US, China, Russia and Greece were found in the eastern Ituri district, the Control Arms Campaign report says.
It highlights the need for a treaty to regulate arms sales, the group says.
The UN is due to vote later this month on starting work on an international arms trade treaty.
The UN imposed an arms embargo on DR Congo's militia groups in 2003.
But the campaign - which also includes Amnesty International and the International Action Network on Small Arms - said small arms made in Russia, China, Serbia and South Africa had also been found in the district.
The munitions were not sold directly but were probably diverted by third parties and arriving via neighbouring countries, the report says.
Jeremy Hobbs of Oxfam International said it was an example of lax arms controls fuelling conflict.
"UN arms embargoes are like dams against tidal waves; alone they can't stop weapons flooding in," he said.
Campaigners want restrictions on the international transfer of weapons that could be used to commit human rights violations, fuel conflict or undermine development.
Irene Khan of Amnesty International said the DR Congo rebels had an "appalling track record" of rights violations including rape and torture.
"That bullets from so many countries have fuelled these abuses is yet another indication that an arms trade treaty must become a reality," she said in a statement.
Four million people are thought to have died in DR Congo's five-year conflict.