The United Nations Security Council and General Assembly have taken the first step toward removing the secrecy around selecting the next U.N. secretary-general, sending a joint letter inviting member states to submit candidates for the post.

The world body is responding to many countries' demands that the successor to Ban Ki-moon, whose term is up at the end of 2016, is chosen with some measure of transparency.

Until now, the selection of the U.N. secretary-general has essentially been determined by the five permanent Security Council members behind closed doors. Now countries will have the chance to openly interview candidates.

The joint letter sent out Tuesday also breaks ground by encouraging U.N. member states to consider nominating women, as every secretary-general over the United Nations' 70 years has been a man.