The U.S. may seek to impose further sanctions on North Korea if Kim Jong Un does not prove his commitment to denuclearization, U.S. National Security Adviser John Bolton said in an interview on Fox Business Tuesday evening.

Praising President Donald Trump’s decision last week “not to agree to a bad deal with North Korea in Hanoi,” Bolton told Lou Dobbs that the U.S. would be watching closely for signs that North Korea is willing to return to the negotiation table.