Former U.N. Secretary-General Kofi Annan is stepping down as the U.N.-Arab League mediator in the 17-month-old Syria conflict at the end of the month, U.N. chief Ban Ki-moon said in a statement on Thursday.

“Mr. Annan has informed me, and the Secretary-General of the League of Arab States, Mr. Nabil Elaraby, of his intention not to renew his mandate when it expires on 31 August 2012,” Ban said in a statement, adding that he and Elaraby were in discussions on appointing a successor to Annan.

“Kofi Annan deserves our profound admiration for the selfless way in which he has put his formidable skills and prestige to this most difficult and potentially thankless of assignments,” Ban said.