One of the close aides to U.N. Secretary-General Ban Ki-moon has quit South Korea‘s foreign ministry as he wants to focus more on his role as special adviser to Ban, Seoul officials said Monday.

Kim Won-soo, a career Korean diplomat, has served as Ban’s deputy chief of staff and special adviser since 2007, when the former South Korean foreign minister took the helm of the U.N., while maintaining employee status at the ministry.

As Ban embarked on his second five-year term as U.N. leader early this month, Kim decided to leave the ministry, a ministry official said.

“Kim tendered his resignation in the middle of this month and his resignation was accepted on Friday,” the official said on the condition of anonymity.

Prior to his appointment to the U.N., Kim served in various capacities at the ministry, including overseas postings at Korean embassies in the United States and India. (Yonhap News)