Amnesty said on Tuesday brokers and transporters from countries including the United States, Britain, Israel and Russia were involved in supplying arms to governments around Africa's Great Lakes region, who were then passing them on to the militias.
The shipments had continued despite a United Nations arms embargo and an ongoing peace process in Democratic Republic of Congo (DRC), the rights group said in a report.
"Armed men are still raping, looting and killing civilians as arms deliveries continue," Kolawole Olaniyan, director of Amnesty's Africa programme, said in a statement.
"If the international community, the UN and neighbouring states fail to halt this proliferation, the fragile peace process will collapse with disastrous consequences for human rights," he said.
The report comes a week before governments, UN agencies and non-governmental organisations meet at United Nations headquarters in New York to discuss the small arms trade.
Congo's civil war left around
4 million people dead
Congo's civil war killed about 4 million people, mainly from war-related hunger and disease, in a nation roughly the size of western Europe. It was officially declared over in 2003, having at one point sucked in six countries.
Despite a peace deal, the resource-rich nation has seen little economic progress and the government has failed to impose its authority over vast areas of the east, where armed groups still pillage and kill with impunity.
Eastern Congo has long been a flashpoint in central Africa's rich Great Lakes region.
Uganda warned last month that armed groups based over the border were planning to attack its territory, while Rwanda has invaded Congo twice in the past decade to attack rebels based there, including some from groups involved in its 1994 genocide.
"International arms flows into the region have been channelled by powerful agents close to the governments of DRC, Rwanda and Uganda to various armed groups and militia in eastern DRC," said Brian Wood, Amnesty's research manager on the arms and security trade.
"International arms flows into the region have been channelled by powerful agents close to the governments of DRC, Rwanda and Uganda to various armed groups and militia in eastern DRC"
Amnesty International research manager on the arms and security trade
Amnesty said it had evidence that up to 400 tonnes of mostly surplus Kalashnikov ammunition had been shipped from Albania and Serbia to Rwanda with the involvement of Israeli, Rwandan, South African and British companies since the end of 2002.
Among other arms transfers, it said it also had evidence of arms-for-diamonds agreements involving the Congolese government and companies in Israel, the Czech Republic and Ukraine.
Many residents in eastern Congo say efforts to stabilise their region are doomed as long as the race for gold and diamonds continues to go unchecked.
Valuable diamonds and gold are
traded for weapons
A British report into gun running in the region in December 2004 said a lack of effective government - leaving borders and airspace largely unpoliced - was a key reason why the 2003 UN arms embargo had failed so dismally.
Amnesty said the UN Security Council needed to renew and strengthen the UN embargo and impose heavy restrictions on any state found to be exporting weapons to armed groups in eastern Congo.
It said airports in the region should be monitored 24 hours a day by UN inspectors.