U.S. Secretary of Defense Mark Esper described North Korea and Iran as "rogue states" that conduct aggressive activities, as the U.S. top nuclear envoy is visiting South Korea. 

Esper made the remarks in a video message sent on Tuesday to thank members of the Department of Defense for their contribution to implementing the National Defense Strategy.

In the message issued ahead of his one-year anniversary in office, Esper listed achievements such as removing terrorists and preserving the freedom of navigation in contested waters.

The Pentagon chief said his department has also deterred aggressive activities perpetrated by rogue states such as North Korea and Iran, as well as near-peers such as Russia and China.

Esper used the word "rogue" to describe North Korea and Iran in February, as well as in December.

His remarks come as U.S. Deputy Secretary of State Stephen Biegun is visiting Seoul this week amid stalled nuclear negotiations between Washington and Pyongyang.

[Photo : YONHAP News]