"Mr. Annan has informed me, and the secretary-general of the League of Arab States, Mr. Nabil El Araby, of his intention not to renew his mandate when it expires on 31 August 2012," U.N. Secretary-General Ban Ki-moon said in a statement.
Annan was appointed special envoy for the Syrian crisis in February to represent both the United Nations and the Arab League. He proposed a six-point peace plan to end the fighting between the regime of President Bashar Assad and the Free Syrian Army that never gained traction on the ground. Both sides have been accused of repeated human rights violations.
Jay Carney, President Obama's press secretary, said that Annan's departure is a result of Assad's failure to abide by promises to follow Annan's peace plan and by the refusal of Russia and China to support meaningful U.N. sanctions. Carney called the Assad regime's attacks on the Syrian opposition "disgusting."
The United Nations estimates more than 10,000 people, mostly civilians, have died since the uprising began with peaceful street demonstrations 17 months ago.
"The hand extended to turn away from violence in favor of dialogue and diplomacy – as spelled out in the six-point plan – has not been taken, even though it still remains the best hope for the people of Syria," Ban said.
The United Nations said Ban would consult with the League of Arab States on a successor for Annan, a former U.N. secretary-general.
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