The suspects, including 10 women, were detained in a crackdown over the past month and were being questioned about attempts to reorganise the Liberation Tigers of Tamil Eelam (LTTE), police spokesman Ajith Rohana said.
"We are questioning them with a view to ensure that there is no resumption of war in this country and to prevent communal violence breaking out," Rohana told reporters in Colombo.
The arrests announced Thursday are the largest in number since Sri Lanka lifted a state of emergency in August 2011.
Government forces declared an end to 37 years of war in 2009 after crushing the LTTE leadership which was fighting for a separate homeland for ethnic minority Tamils.
Since then, no attacks have been carried out by the rebels, but authorities have issued warnings that they may try to regroup.
Rohana said the 60 suspects were being held at a detention centre in the southern town of Boossa and another in Vavuniya, just outside the former northern war zone.
No other deta