James Smith, the chief executive of the Aegis Trust, which campaigns against genocide, made the charge a day after the Sudanese government said it didn't want U.N. peacekeepers and told the 7,000-strong African Union force to leave, The Times of London reported.
"By crippling that lifeline, the government of Sudan is deliberately inflicting on the group conditions of life calculated to bring about its physical destruction," Smith said. "Under the terms of the United Nations Genocide Convention, this constitutes genocide."
Darfur's rebels took up arms in 2003, claiming the government was neglecting the region. Khartoum sent in its own army and enlisted militias to help quell the uprising.
More than 250,000 people have died from fighting, disease or hunger, and more than 2 million live in refugee camps, aid officials say.
Khartoum plans to send 10,000 of its own troops to Darfur as part of a peace force, but aid workers claim soldiers have been responsible for some of the worst atrocities, the report said.
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