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 in 2012 two Italian marines on suspicion they killed two fishermen that they had mistaken for pirates while they had been escorting an oil tanker.

One of the pair returned to Italy with health problems, but India has refused to let the other man, Salvatore Girone, leave the country.

The case has soured relations between India and Italy, but the two countries agreed last year to move the case 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 be in immediate contact with India to try to make sure he would return as soon as possible. The court will continue to review the merits of the case against the two marines.