New Delhi  - A woman convicted of assassinating former Indian prime minister Rajiv Gandhi has begun an "indefinite fast" to demand her immediate release from jail, news reports said Tuesday.

Nalini Sriharan, 43, started the fast Monday in a prison in the southern state of Tamil Nadu and said she was to continue her protest until she is released from prison, the NDTV network reported.

In a petition filed before the Chennai High Court last week, Nalini said she had spent 18 years in jail and was entitled to release in 2005.

She began the protest to demand that an advisory panel that was to decide on her release be set up as soon as possible.

Rajiv Gandhi was killed in a suicide bombing by Sri Lanka's separatist rebel Liberation Tigers of Tamil Eelam in May 1991. Indian security agencies that unravelled the plot found Sriharan was part of the assassination squad.

Sriharan was one of four people initially given a death sentence for taking part in the assassination.

Later, at the intervention of Gandhi's widow, Sonia Gandhi, who heads India's ruling United Progressive Alliance, the death sentence was commuted to life imprisonment.

In 2006, the Tamil Tigers, which had originally denied any hand in Gandhi's killing, took responsibility for the assassination and expressed "regret" for the "monumental historical tragedy."

Sriharan's husband and co-convict, Murugan, is also serving his sentence in the same prison. Hopes for Sriharan's early release brightened after the slain prime minister's daughter Priyanka Gandhi met her in prison.

Priyanka, who was a teenager when her father was killed, said in interviews that she had forgiven her father's killer.

"I would like to settle down peacefully. ... I am already 43," said Sriharan, in her plea to the court. "Due to my health condition after 18 years in jail, I cannot expect to live long."  dpa