Lakhdar Brahimi, the veteran U.N. mediator tapped to help broker a political settlement in Syria, resigned Tuesday, signaling the bleak prospects for peace in a conflict that has gone on for more than three years.

“I have decided to accept the request of Lakhdar Brahimi to relinquish his duties,” Secretary-General Ban Ki-moon said at a news briefing at the United Nations.

The resignation takes effect at the end of May.

“Brahimi has long been recognized as one of the world’s most brilliant diplomats,” Ban said. Brahimi’s exit, he said, “is a failure for all of us.”

Brahimi thanked Ban and told reporters the resignation “was not a very pleasant situation for me.”

His resignation came amid rising frustration with President Bashar Assad of Syria, who ignored Brahimi’s agenda for talks and then scheduled a presidential election that will probably give him another seven-year term. Top U.N. officials said the election would probably sabotage further diplomacy.

New York Times