India has barred Italy’s ambassador from leaving the country as tensions between the two nations deepen.

Italy had refused to allow the extradition of two Italian marines accused of shooting dead two fishermen off India’s southeastern coast.

Delhi had summoned Italian ambassador Daniele Mancini this week to protest against Rome’s decision not to return the marines to stand trial over the killings of the fishermen while on anti-piracy duty last year, reports The Associated Press.

The Supreme Court ordered the Italian envoy not to leave India and demanded an explanation as to why Italy reneged on its promise to return the marines, who were allowed to fly home to vote in the recent general election.

The court has sought a reply from the ambassador by March 18, said Viplav Sharma, defense counsel for the two marines.

Massimiliano Latorre and Salvatore Girone were part of a military security team when they opened fired on a fishing boat, which they claim they mistook for a pirate vessel, killing the two fishermen.

Italy refused to return the two marines to face trial in India, claiming it would violate their rights, the Italian Foreign Ministry said Monday. Italy dismissed Indian claims of jurisdiction to try the marines, insisting the shooting occurred in international waters.

G.E. Vahanvati, India’s attorney-general, said Delhi was “extremely concerned” by Rome’s move, saying it was a “breach of undertaking given to the highest court of the land”, the Financial Times reports.

Prime Minister Manmohan Singh accused Italy of violating “every rule of diplomatic discourse” and warned that if the sailors did not return “there will be consequences for our relations with Italy”, according to AP.