U.N. Secretary General Ban Ki-moon is poised to appoint Tadamichi Yamamoto, deputy head of the U.N. Assistance Mission in Afghanistan, as new chief of the mission and his special representative to the country, U.N. sources said Thursday.

The appointment of Yamamoto, 65, a former diplomat, is expected to be announced soon, with the U.N. Security Council likely to approve it, the sources said.

If formalized, Yamamoto will be the third Japanese national to serve as special representative to a U.N. chief, following Yasushi Akashi and Sukehiro Hasegawa, who headed the U.N. Transitional Authority in Cambodia from 1992 to 1993 and the U.N. Mission of Support to East Timor from 2004 to 2006, respectively.

Yamamoto served as Japan's ambassador for assistance to Afghanistan and Pakistan between 2010 and 2012. He coordinated a ministerial-level international conference on Afghan development held in Tokyo in July 2012.

The deputy chief of UNAMA since November 2014, Yamamoto held such Foreign Ministry posts as ambassador in charge of the North Korean nuclear issue, ambassador of Japan's permanent mission to UNESCO, and also ambassador to Hungary.