BEIJING (AP) — Authorities have given no word on the status of Chinese legal rights activist Guo Feixiong after he was blocked from leaving the country last week to join his family in the United States, his sister said Tuesday.

Yang Maoping said they had no word from Guo or information from police since he was reportedly detained at Shanghai’s Pudong airport Thursday while attempting to board a flight to the U.S.

Guo had messaged friends that he would go on hunger strike unless allowed to leave the country to be with his wife who is undergoing treatment for cancer.

“I have been informed that I cannot leave the country because I am under suspicion of endangering state security and other such charges. I will now go on indefinite hunger strike and call on the people of China and governments and people around the world to offer assistance," Guo said in a text sent to friends and passed on to journalists.

As a lawyer, Guo represented government critics and had been imprisoned for more than 10 years under China’s loosely defined state security laws. The ruling Communist Party frequently uses travel bans to punish those who challenge it, often as a prelude to prosecution and lengthy prison terms.

Yang said Guo's concern over his wife's health had pushed him to risk another confrontation with authority.

“The lack of information on top of her health situation is very distressing," Yang said.