"They ended their protest following an assurance that the grievances would be addressed by 7 November," Rohana Pushpakumara the Commissioner General of Prisons said.
Pushpakumara said Sirisena's message was conveyed to the fasting inmates by the leader of the opposition R Sampanthan and other Tamil parliamentarians.
Justice Minister Wijeyadasa Rajapakshe had visited them on Thursday with a pledge to resolve the issue.
Hundreds of ethnic Tamils have been lodged in jails without trial since 2009, when Sri Lanka's military crushed Liberation Tigers of Tamil Eelam (LTTE) rebels in a decades- long conflict for control of the island's northern Jaffna peninsula.