South Korea’s intelligence cooperation with the U.S. has become one of the most difficult issues in bilateral relations, Seoul’s ambassador told lawmakers on Monday, confirming that Washington raised concerns about the unification’s minister’s remarks on a suspected North Korean uranium enrichment facility.

Ambassador Kang Kyung-wha made the remarks during the National Assembly’s audit of the South Korean Embassy in Washington. She confirmed that intelligence cooperation was discussed during a Sept. 18 meeting between U.S. Secretary of State Marco Rubio and South Korean Foreign Minister Cho Hyun.

Independent lawmaker Han Dong-hoon asked whether Rubio had conveyed that trust in South