It is not clear why Mrs Feng failed to fill in the forms and transfer her residence. She has complained on Weibo, China's version of Twitter, that she was not warned of the consequences until it was too late. But as her pregnancy progressed, local officials offered her family a deal: pay 40,000 yuan to smooth the bureaucracy over.

When the couple said they did not have the money, Mrs Feng was taken from her home on May 30 by more than 20 officials and ransomed, her husband said. The officials held her for three days, apparently sending threatening text messages to members of her family, before giving the foetus a lethal injection on June 2.

''It should not be a cent less than that [40,000 yuan],'' read one text message, allegedly sent by Yuan Fang, a family planning official, to Mr Deng's sister, Deng Yan. A photograph of the message on what appears to be a smartphone has been posted by the family to HSW.cn, a local Shaanxi internet portal by the family.

''I told your father this already and he said he did not have the money, so we did not have a choice. It is you guys that have been careless,'' the message continued. Mr Deng said he had tried to raise the money until the last minute, but had failed.

''At the hospital they held her down,'' said Mr Deng to All Girls Allowed, a Christian organisation in the United States that campaigns against the one-child policy. ''They covered her head with a pillowcase. She could not do anything because they were restraining her.'' He said his wife had tried to kill herself after the abortion.