Top U.S. nuclear negotiator Christopher Hill says he is concerned about North Korea’s recent moves that suggest it might test-fire a ballistic missile.

He made the remarks after arriving in Tokyo Monday afternoon as part of the entourage accompanying Secretary of State Hillary Clinton on her trip to Asia.

Hill said concerned nations should discuss the North’s moves as soon as possible, hinting that the issue will be part of Clinton’s agenda during her talks with South Korean, Chinese and Japanese officials.

Clinton will arrive in Tokyo Monday evening for a meeting with Japanese Foreign Minister Hirofumi Nakasone.