Anti-CAA activist Akhil Gogoi in a letter from jail on Tuesday alleged physical and mental torture in custody and claimed that he was offered instant bail by NIA interrogators if he joined either the RSS or BJP.

The letter released by Gogoi's newly floated political outfit Raijor Dal said that the peasant leader was taken to Delhi on December 18, 2019 without the Court's permission.

"At the NIA headquarter, I was lodged in lockup no 1 and was given only one dirty blanket. I slept on the floor in 3-4 degree celsius of temperature," he claimed.

During interrogation, the NIA officials offered him instant bail if he joined the RSS, the letter claimed.

"When I was arguing against the insulting offer, they came out with another proposal of joining the BJP. They said I could contest the Assembly against a vacant seat and become a minister," Gogoi claimed.

The RTI activist also alleged that he was offered Rs 20 crore to start an NGO by leaving the peasant body Krishak Mukti Sangram Samiti (KMSS) and work against conversion of Assamese people into Christianity.

"When I did not accept any of their proposals, they offered me a meeting with the chief minister and an influential minister of Assam. I turned down that too," Gogoi said.

He alleged that when he accepted none of the NIA offers of the NIA, he was called a "disobedient citizen" as charged in extreme cases.

"I was threatened with dire consequences if I don't accept their proposals. Death threats also came. I was threatened with at least 10 years of imprisonment. With so much physical and mental torture, I became restless on the night of December 20," Ggogi wrote.

He was admitted to Gauhati Medical College and Hospital for treating COVID-19 and remains there for other ailments.

The NIA had arrested him in December 2019 for his alleged role in violent anti-Citizenship Amendment Act protests.