About 300 Tamil political prisoners in 11 prisons began a hunger strike on October 12.
Many of the prisoners have been detained without trial under the Prevention of Terrorism Act. Some have been in jail for up to 20 years.
They are accused of being members of the Liberation Tigers of Tamil Eelam (LTTE), which fought for an independent Tamil homeland in the north and east of the island of Sri Lanka, but was defeated in 2009.