Farhad Mazhar, one of Bangladesh’s most prominent government critics, went missing on Monday, after calling up his wife to tell her that he was being taken away by a man, AFP reported, quoting police officials. Mazhar told his wife he thought he may be killed, before disappearing.

Later, she received a call demanding ransom of 35 lakh taka (Rs 28.1 lakh) for her husband, police officials said. Police said they had not yet registered a case as the family had not formally reported him missing.

CCTV footage of Mazhar’s neighbourhood in Dhaka showed him walking away with a man early in the morning. The 69-year-old writer is a supporter of the main opposition party in Bangladesh, the Bangladesh Nationalist Party.

A Rapid Action Battalion-6 team began a rescue operation at a street in Khulna city since Monday evening to find Mazhar, the Dhaka Tribune reported. RAB 6 Director Khandker Rafiqul Islam said that they were able to trace Mazhar’s mobile phone to near the KDA Approach Street in Khulna. “Currently we are searching every house in this street [KDA Approach] and the Ibrahim Street beside this one,” the director said.

Meanwhile, BNP Joint Secretary General Ruhul Kabir Rizvi alleged that officials of the government’s law enforcement agencies picked up Farhad Mazhar. As the government is scared of his write-ups, it targeted him,” he alleged.

BNP officials claim that tens of thousands of their activists and supporters have been arrested by the government since 2014, when the party boycotted the general election over fears it would be rigged. There have also been allegations that authorities detained BNP supporters and held them in secret jails.