Image by youtube American student Otto Warmbier was imprisoned in North Korea for over a year.

The parents of U.S. college student Otto Warmbier sued North Korea on Thursday over their son’s death in 2017 following his release from captivity there, according to the lawsuit filed in U.S. District Court.

The wrongful-death suit comes at a diplomatically delicate time, just weeks ahead of an expected meeting between North Korean leader Kim Jong Un and U.S. President Donald Trump. Kim and South Korean President Moon Jae-in also are set to meet on Friday.

“Otto was taken hostage, kept as a prisoner for political purposes, used as a pawn and singled out for exceptionally harsh and brutal treatment by Kim Jong Un,” his father Fred Warmbier said in a statement. “Kim and his regime have portrayed themselves as innocent, while they intentionally destroyed our son’s life. This lawsuit is another step in holding North Korea accountable for its barbaric treatment of Otto and our family.”

Warmbier, a 22-year-old student from Wyoming, Ohio, was imprisoned in North Korea from January 2016 until he returned to the United States in a coma. He died a few days after his return, and an Ohio coroner blamed lack of oxygen and blood to the brain. North Korea blamed botulism and ingestion of a sleeping pill and dismissed torture claims.

“North Korea, which is a rogue regime, took Otto hostage for its own wrongful ends and brutally tortured and murdered him,” the wrongful-death lawsuit said.