SYDNEY, Australia — Chinese officials have cut off all contact between a detained Australian writer and democracy activist, Yang Hengjun, and his family, in what his lawyers described on Sunday as an effort to “break” Mr. Yang and force him to confess to being a spy.

Mr. Yang, who was detained in January after arriving in Guangzhou, China, on a flight from New York, has consistently denied the charge.

Mr. Yang’s lawyers said they had confirmed that Chinese officials were conducting daily interrogations of him in isolation, shackling his ankles and wrists, refusing to allow access to any messages of support from relatives or friends and giving him at least nine pills a day for supposed health problems like high blood pressure and kidney complications.

“We’re concerned because he went in as a fit and healthy man,” Sarah Condon, one of his lawyers in Melbourne, Australia, said in an interview. “Now he has this purported diagnosis and is being fed a concoction of drugs.”