The U.N.-Arab League special envoy to Syria, Kofi Annan, has announced his resignation after failing to bring an end to more than a year of violence. On Thursday, Annan said both sides, particularly the Syrian government, had failed to respect his ceasefire plan.

Kofi Annan: “The increasing militarization on the ground and the clear lack of unity in the Security Council have fundamentally changed the circumstances for the effective exercise of my role. Yet the bloodshed continues, most of all because of Syrian government’s intransigence and continuing refusal to implement the six-point plan, and also because of the escalating military campaign of the opposition, all of which is compounded by the disunity of the international community.”

Annan’s resignation will take effect at the end of the month. His departure comes amidst fierce clashes in Aleppo, where rebels say they now control more than half of the city.