The nominee for the U.S. deputy secretary of state expressed concern that North Korea appears to lack interest in diplomacy with the United States and Washington must therefore focus even more on deterrence.

Kurt Campbell, currently the National Security Council coordinator for Indo-Pacific affairs, made the remarks during a Senate confirmation hearing on Thursday.

Campbell said that following the U.S.’ last constructive diplomatic engagement with North Korea was the aborted meeting in Vietnam between Kim Jong-un and Donald Trump, Pyongyang has rebuffed every effort by Washington to establish contact.

The nominee said that the U.S. attempted creative and inventive approaches with the North, citing an offer to provide COVID-19 vaccines during the pandemic and engagements on humanitarian grounds.

Campbell added, however, that the U.S. has been stonewalled in its attempts to deliver letters or set up meetings.

The nominee also expressed concerns that North Korea continues to perfect its long-range missile and nuclear capabilities in ways that are antithetical not only to the region but also to the U.S. as well, and pursuing a dangerous path with its provision of arms in its military cooperation with Russia.