NEW YORK 

UN Secretary-General Ban Ki-moon has appointed Ismail Ould Cheikh Ahmed of Mauritania as his special envoy for Yemen, the UN spokesperson's office said Saturday.

Ahmed, who currently leads the UN’s Ebola response mission, replaces Jamal Benomar of Morocco, who resigned on April 15 after four years in office.

"[Ban] expresses his sincerest gratitude to Mr. Benomar for his tireless efforts aimed at assisting the Yemeni people in realising their aspirations for change through a peaceful transition," the spokesperson's office said in a statement.

Benomar has worked on mediating negotiations among Yemen's rival factions since 2011, when a wave of popular demonstrations took place across the Arab world. A year later, a popular uprising ended the rule of longstanding Yemeni President Ali Abdullah Saleh.

Although talks led to a national partnership agreement to give more power to regions, Shiite Houthi rebels in the north openly turned against the process as they complained it isolated them.

The Mauritanian diplomat comes to the job as a dramatic escalation of violence interrupted the talks altogether following the September 2014 takeover of government institutions and parts of the country by the Houthis.

The crisis prompted a Saudi-led coalition of Arab states to launch a bombing campaign on March 25 against the Shiite group.

The coalition declared an end to the campaign on Tuesday, but said it would continue to strike Houthi positions "if necessary."

The UN estimates at least 551 civilians were killed in the past four weeks.