In a case that poisoned ties between the two countries, Salvatore Girone and Massimiliano Latorre spent years facing charges in India for shooting the fishermen when their boat neared the Italian oil tanker MV Enrica Lexie off the Kerala coast.

Italy took the issue to the Permanent Court of Arbitration in The Hague in 2015, saying that the tribunal should hear the case under maritime law as the incident happened in international waters off India's southern coast.

But New Delhi insists that the two marines -- one of whom was allowed home in 2014 and the other in 2016 -- should both return to India for a final judgement by an Indian court.

"India and its fishermen are the true victims in this case," Indian representative G. Balasubramanian told the court in The Hague.

Insisting that the incident happened in India's "exclusive economic zone", he added that the "quick efforts of the Indian authorities deserve not criticism as was levelled by Italy, but praise."

Italy's representative Francesco Azzarello however said India had no right to arrest the marines.

He said the Girone and Latorre were stationed on the tanker because the region was prone to piracy, and said they had fired on the fishing boat because it failed to heed warnings to stay away.

"As members of the Italian armed forces, they were state officials, performing official duties at the time of the incident, under Italian law," Azzarello told the court.

Italy says India also overstepped the mark by sending armed vessels with air support to escort the men to the port of Cochin, where Indian forces boarded the tanker and arrested them.

Latorre was allowed to return to Italy in 2014 after suffering a stroke. Girone was permitted to do the same in 2016 after living in Italy's embassy in Delhi for four years.

The detention of the marines, the murder charges and the long wait for the case to be resolved are sore subjects in Italy.

In December 2014 Rome threatened to withdraw its ambassador from India after a court rejected Latorre's original request for medical leave.