SEOUL, South Korea — President Trump has sent a letter to North Korea’s leader, Kim Jong-un, expressing his willingness to help the North battle the coronavirus, North Korea said on Sunday.

“I would like to extend sincere gratitude to the U.S. president for sending his invariable faith to the Chairman,” said Kim Yo-jong, the North Korean leader’s sister and policy aide, in a statement carried by the North’s state-run Korean​ Central​ News Agency. Ms. Kim lauded Mr. Trump’s decision to write the letter as “a good judgment and proper action.”

In the letter, Mr. Trump “wished the family of the Chairman and our people well-being,” Ms. Kim said, referring to her brother by one of his official titles.

According to Ms. Kim, Mr. Trump also explained his plan to move relations between the two countries forward and “expressed his intent to render cooperation in the anti-epidemic work, saying that he was impressed by the efforts made by the Chairman to defend his people from the serious threat of the epidemic.”