A UN arbitration court has ruled that India should release an Italian marine who has been detained in Delhi for more than four years, and allow him to return home, the Italian Foreign Ministry said on Monday.

India arrested two Italian marines in 2012 on suspicion of killing two fishermen while assigned to an anti-piracy mission on an Italian oil tanker. One returned to Italy with health problems, but India has refused to let the other, Salvatore Girone, go. He is living in the Italian embassy in Delhi.

"This really is a significant step forward which we have worked on with great dedication," Prime Minister Matteo Renzi told reporters. "I'll take advantage of this moment to send a message of friendship to the great people of India."

The case has soured relations between India and Italy, but they agreed last year to move proceedings to the Permanent Court of Arbitration in The Hague and abide by its decisions.

The Italian Foreign Ministry said in a statement that in an initial ruling, the court had decided that Girone should be allowed home. It said it would now contact India to try to make sure he could return as soon as possible.

No one was immediately available to comment from either the Indian Foreign Ministry in Delhi or The Hague.

The UN court will continue to review the merits of the case and no date has been set for a definitive ruling.

"The government underlines that today's court decision concerning the measures requested by Italy on behalf of Sergeant Girone will not influence the progress of the arbitration procedures, which should decide if Italy or India has jurisdiction in the case," Italy's Foreign Ministry said.

Italy has argued that the case should not be heard in India because the incident occurred in international waters.

Marines are viewed by Italy as state officials immune to foreign prosecution. Italy has paid $190,000 in compensation to each victim's family.  - Reuters