"I'll be in the court, to symbolise and mark physically the determination of Italy to solve this case, a sentiment manifested in a very clear way also recently by our president (Giorgio Napolitano)," De Mistura said Sunday to Italian journalists gathered in the Italian embassy.
The move was aimed to, "demonstrate the level of indignation and determination of the Italian Republic and to show to the Indian judicial side that Italy requires that this matter be finally answered," he is quoted as saying by the agency.
The European Commission has said the issue of the Italian marines may have an "impact" on the European Union-India relations and "will be assessed carefully". Last week, Italian Premier Enrico Letta said that Italy will work among its international partners to raise awareness of the plight of the marines.
Napolitano has said that the case had been managed in "contradictory, disconcerting ways by the Indian authorities".