The United States on Monday sanctioned three North Korean officials, including a top aide to North Korean leader Kim Jong Un, citing “ongoing and serious human rights abuses and censorship,” the U.S. Treasury Department said, Reuters reported.

The sanctions “shine a spotlight on North Korea’s reprehensible treatment of those in North Korea, and serve as a reminder of North Korea’s brutal treatment of U.S. citizen Otto Warmbier,” the department said in a statement.

Warmbier was an American student who died in June 2017 after 17 months of detention in North Korea, which contributed to already tense exchanges between Pyongyang and Washington, primarily over North Korea’s nuclear development programme.

It was not clear whether the decision to sanction the three men was related to U.S.-North Korean nuclear diplomacy, which has made little obvious progress since U.S. President Donald Trump and North Korean leader Kim met in Singapore in June.

The Treasury identified the three as Ryong Hae Choe, an aide close to Kim who heads the Workers’ Party of Korea Organization and Guidance Department; State Security Minister Kyong Thaek Jong and the director of North Korea’s Propaganda and Agitation Department, Kwang Ho Pak.