BEIJING — A Chinese dissident writer said Monday that police in his hometown are holding three of his siblings in retaliation for an article he wrote condemning the detention of a fellow writer linked to the investigation of an anonymous letter online calling for the Chinese president’s resignation.

Zhang Ping, better known by his penname Chang Ping, said by phone from his home in Germany that his two younger brothers and a younger sister were detained after they returned to the southwestern town of Duofu to celebrate their father’s birthday Sunday and pay respects at the tombs of their ancestors.

Zhang said police were demanding that he cease his political writing and give up his column on the website of German international broadcaster Deutsche Welle. He said police also told family members that they want him to remove the critical essay about the detained writer from the website.

“It’s horrific that a local Chinese police station should stretch its arm toward German media and demand an article be removed,” Zhang said. “That’s interference with press freedom.”

Asked by phone about Zhang’s siblings, Duofu police said they were holding several people on suspicion of causing a fire while paying their respects to their ancestors but refused to give details. Zhang said it was common for people to set off fireworks when visiting ancestors’ tombs and believed there was no real damage. He said police were simply using that as a pretext to hold his brothers and sister.

Zhang had criticized the disappearance of writer Jia Jia over suspicions that he was linked to the posting of a letter that criticized President Xi Jinping’s rule and called for him to step down. The letter, signed by “loyal Communist Party members,” briefly appeared on the government-controlled news site Watching.cn in early March.

Beijing appears to have launched a concerted hunt for those responsible for the letter, in a reflection of the leadership’s anxiety about any form of dissent, including within the party itself.

Jia was later confirmed to be in police custody and released after 10 days. He has since declined to speak to the media about the case.

The president of Watching.cn, Li Wanhui, two top editors and two site technicians have also dropped from view for days and are believed to be under investigation. Nine other technicians working for a technology company that provides support to the site also are reported missing.

Similar to Zhang, another prominent overseas Chinese activist, Wen Yunchao, also has said that authorities in his southern Chinese home county of Jiexi have been holding his elderly parents and a younger brother since Tuesday in an apparent attempt to pressure him into admitting involvement in posting the letter. Wen has denied any ties to the letter.

The human rights group Amnesty International has urged Chinese authorities not to harass dissents’ family members, saying such actions undercut China’s claim to respect the rule of law.

On Monday, Zhang said he would not give up writing, but would distance himself from his family members back in China.

“To negotiate with the authorities is like negotiating with gangsters,” Zhang said. “It’s impossible for me to give up writing.”

“My relatives are innocent, and it’s against Chinese law to involve them over me,” he said.

Chinese authorities have in the past targeted him and his wife and child, but they started harassing his siblings about a week ago with phone calls and home visits, Zhang said.

“The intimidation apparently has escalated because of the anonymous letter,” he said.