India's Supreme Court Friday gave the go-ahead to the country's top anti-terror agency to investigate the case of two Italian marines accused of killing two Indian fishermen off the coast of the southern state of Kerala in February last year.

A three-judge bench, headed by Chief Justice Altamas Kabir, allowed the National Investigation Agency, instead of the police, to probe the case of the two Italian marines and also directed a special court to complete the trial at the earliest.

The two marines -- Massimiliano Latorre and Salvatore Girone -- allegedly shot dead the two Indian fishermen from on board an Italian oil vessel which they were guarding off the Kerala coast at the time, after mistaking them for pirates.

The duo, arrested after the incident and subsequently released on bail, are currently in the national capital facing trial in the case. They have been charged with murder which carries a maximum of death penalty in India.

The case has sparked a diplomatic row between India and Italy, which soured particularly after Rome refused to send back the two marines to India to face trial last month. The duo were allowed by the apex court to go to Italy this February to cast their vote in their country's general elections.

The marines, however, returned to India on March 22, after the Italian government received assurances about their human rights.

Italy insists the incident took place in international waters and so the marines be tried in a global court, a claim dismissed by India which says the shooting happened in its territorial waters.