Kofi Annan, the U.N.-Arab League envoy for Syria, announced his resignation Thursday, the Washington Post said.
Annan, 74, said he will officially resign at the end of August due to the U.N. Security Council's failure to negotiate a peaceful resolution to the ongoing civil war in Syria, the Washington Post said.
"Without serious, purposeful and united international pressure, including from the powers of the region, it is impossible for me, or anyone, to compel the Syrian government in the first place, and also the opposition, to take the steps necessary to begin a political process," Annan said to the New York Times.
According to the New York Times, Annan also wrote an opinion article that was posted on the Web site of the Financial Times and headlines, "My Departing Advice on How to Save Syria." In the article, Annan criticized all parties involved in the conflict and called the Syrian government "40 years of dictatorship."
Annan's resignation comes nearly two weeks after Russia and China vetoed a resolution that would have enforced sanctions on the Syrian government and strengthened Annan's mediation efforts, the Washington Post said. The veto allowed the Syrian conflict to reach an even more violent stage.
Annan also negotiated a six-point peace plan in March that Syrian President Bahar-al Assad promised to abide by, the New York Times said. However, the Syrian government never implemented the plan.
All of these actions grouped together ultimately frustrated Annan to the point of resignation, the New York Times said.
The U.N. has not announced who will replace Annan when his mandate expires at the end of August, and neither Assad or any Syrian opposition forces have released statements about his departure.