The government's refusal came as two other videos showing alleged abuses by DR Congo soldiers began circulating on social media networks.
The seven-minute video that emerged over the weekend shows a group of uniformed men opening fire, then walking among at least 20 bodies, apparently in the violence-wracked central Kasai region.
Washington and Paris both called on the government to open an inquiry, with a US State Department spokesman condemning the "heinous abuses" seen in the video.
But Kinshasha, saying it was routinely the target of "malicious rumours", brushed off the demands.
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In a statement calling the video the work of "anonymous amateurs", the government said "it is not our job to prove the innocence of the FARDC", the name of DR Congo's armed forces.
"It's up to the accusers, unknown for now, to prove these facts so that all implicated parties can respond, in line with the law."
But a government spokesman, Lambert Mende, said yesterday that they were not being charged with war crimes or crimes against humanity, but "violations of orders" and "extortion" during an operation in Mwanza Lomba, the Kasai village where the video was filmed.
The Kasai region has been plagued by violence since mid-August when government forces killed a tribal chief and militia leader, Kamwina Nsapu, who had rebelled against the central government.
At least 200 people have been killed since then, leading the UN mission in the country to pledge at least 100 peacekeepers for the region.