"We will honour assurance given to Italy," Singh told reporters here.
Informed sources here said the National Investigation Agency (NIA), which is probing the case, would not press for death sentence against the marines - Massimiliano Lattore and Salvatore Girone.
Italian Prime Minister Mario Monti called up External Affairs Minister Salman Khurshid Friday after NIA registered a case against Italian marines.
Italian Deputy Foreign Minister Staffan de Mistura, too, called on Khurshid after NIA initiated its probe.
Khurshid had said last month after the return of the two marines to the country that India has given an assurance to Italy that the marines will not face death penalty if they return by the deadline set by the Supreme Court.
The home ministry handed over the case to the NIA, which filed a first information report (FIR) before the designated special NIA court.
The sources said NIA had booked the marines in its FIR under various sections including murder and attempt to murder.
They said NIA had also booked the marines under the Suppression of Unlawful Acts Against Safety of Maritime Navigation and Fixed Platforms on Continental Shelf Act, 2002.
The two marines, on board the Italian cargo vessel Enrica Lexie, had allegedly shot dead two Indian fishermen Feb 15 last year suspecting them to be pirates.