U.N. Secretary-General Ban Ki-moon on Wednesday named Slovak diplomat Jan Kubis as his next special envoy to Afghanistan, a challenging post that will be changing hands for the third time in four years.

Kubis will replace Staffan de Mistura of Sweden, whose tenure expires on December 31.

Kubis, 59, who speaks five languages and graduated from a Moscow international relations institute, is a former Slovakian foreign minister who also has had a lengthy career as an international official.

Most recently he has been head of the U.N. Economic Commission for Europe.

The United Nations has no peacekeepers in Afghanistan, where U.S. and NATO troops are battling Taliban insurgents. The U.N. mission, known as UNAMA, engages in political support and aid work, compiling closely watched reports on civilian casualty figures from the Afghan conflict.

The U.N. announcement of Kubis's appointment described the Afghanistan job as one of the most challenging duty stations. Seven U.N. staff were killed in April in an attack on the U.N. compound in the northern city of Mazar-i-Sharif.

The post also has been politically controversial. De Mistura's predecessor, Kai Eide of Norway, became involved in a dispute with his U.S. deputy Peter Galbraith over the conduct of elections in Afghanistan, which ended with Galbraith being fired.

Eide's predecessor, Tom Koenigs of Germany, was criticized by some Western diplomats at the United Nations as ineffectual. De Mistura has largely avoided controversy since taking over the job in March of last year.

(Reporting by Patrick Worsnip; editing by Bill Trott)