Top climate change official to quit his post following failed struggle for global deal

But Mr De Boer said his decision was not linked to the result of December's Copenhagen conference which ended without a legally binding agreement on global emissions.

He said he began looking for another job before then.

His resignation takes effect from July 1, five months before 193 nations are due to reconvene in Mexico for another attempt to reach a worldwide agreement on controlling greenhouse gases.

Mr De Boer said he believed talks on a new treaty were on track, despite the frustration of failing to reach a deal at Copenhagen in December.

He said he was announcing his departure now to allow UN Secretary General Ban Ki-moon to find a successor well before the Mexico conference.

The former Dutch civil servant and climate negotiator was widely credited with raising the profile of climate issues.

But his constant travel and frenetic diplomacy failed to bridge the suspicions and distrust between developing and industrial countries that barred the way to a final agreement at the Copenhagen summit.

A partial agreement reached in Copenhagen, brokered by President Barack Obama, "was very significant," he said.