‍China’s Taiwan Affairs Office said on Sunday that they had sent a letter written by detained Taiwanese resident Lee Ming-cheh to his family after reports said Lee’s wife intended to visit the mainland and to appeal to the release of her husband.

Based on humanitarian considerations, the Association for Relations Across the Taiwan Straits (ARATS) delivered Lee's letter addressing to his wife and parents to Taiwanese authorities on April 7, Taiwan Affairs Office said in a statement, adding the investigation is still ongoing.

Last week, the office confirmed Lee’s detainment. The spokesman of Taiwan Affairs Office, Ma Xiaoguang, said the Taiwanese resident participated in activities endangering national security.

He added that Lee was in good condition, without giving further details.

Lee’s wife, Lee Ching-yu, told Taiwanese media that she planned to visit the mainland on Monday and to appeal to release his husband.

Lee reportedly went missing on March 19, after he boarded a flight from Taipei to Macao.