The U.N. chief has appointed a new special envoy to Yemen as pressure grows to return to talks in search of a political solution to the country's crisis.

A statement Saturday says Ban Ki-moon has appointed Ismail Ould Cheikh Ahmed of Mauritania, who until now has led the U.N.'s Ebola mission.

Ahmed replaces Jamal Benomar, who had said he was stepping down. Benomar had faced sharp criticism from Saudi Arabia and other Gulf countries as his efforts to broker peace showed little recent success.

More than 1,000 people have been killed in recent weeks after Iran-backed Shiite rebels swept through Yemen and a Saudi-led Sunni coalition began airstrikes to drive them back.

Benomar in 2011 had been tasked with guiding a peaceful transition for Yemen after the Arab Spring.