Amnesty International says many of the countries now backing this year's protests in the Middle East also supplied some of the weapons used against demonstrators.
In a fresh report, Amnesty studied arms transfers to Egypt, Libya, Yemen, Syria and Bahrain since 2005.
Amnesty said among the main arms suppliers to these countries were Russia, the United States, France and Germany, as well as the Czech Republic and Bulgaria.
Amnesty said many of the heavy weapons found in Libya by the human rights organization's researchers were either from Russia or from the former Soviet Union, such as Grad rockets which Amnesty described as "inherently indiscriminate."
The group says countries must tighten arms export controls to avoid the risk that weapons will be used to violate human rights.
The report comes as the human rights group urges the U.S. Congress to block a $53 million proposed arms sale to Bahrain where security forces have killed more than 30 protesters.
In response, U.S. State Department spokesman Mark Toner said a final decision on the arms sale had not been made, and noted many members of Congress had expressed concern about the deal.
"We're going to continue to look at all the elements on the ground, including the human rights situation," Toner told reporters.
Toner refused to speculate on whether the sale could be scrapped if the Bahraini government fails to implement reforms. But he did say the United States would study an independent Bahraini report on alleged human rights violations expected to be released soon.
compiled from agency reports