India summoned the Italian ambassador on Tuesday to demand that Rome hand over two of its marines facing trial for the killing of two fishermen, an Indian foreign ministry statement said.
The marines are accused of shooting dead two fishermen off India's southwestern coast in February last year, when their fishing boat came close to the Italian oil tanker they were guarding.
The marines said that they mistook the fishermen near the port of Kochi for pirates. They were granted leave by India's top court to return home for four weeks in order to vote in the February 24-25 national elections.
India's foreign secretary Ranjan Mathai met with the Italian ambassador Daniele Mancini and said Rome "was obliged to ensure their return to India", a day after officials said that the men would not be coming back to Delhi.
India's demand was conveyed to Mancini in the "strongest terms," the statement issued by the foreign ministry said.
The marines were allowed to go home last month by India's Supreme Court, after Italy gave an undertaking that they would return to face trial once their leave expired at the end of March.
"The government of India states firmly that it does not agree with the position conveyed by the Italian government on the return of the two marines to India," the ministry statement said.
"India expects the Republic of Italy as a country that is committed to the rule of law to fulfil the sovereign undertaking given by it to the Supreme Court of India."
The case, which was transferred from a local court in India's southern Kerala state to the Supreme Court in New Delhi, has created diplomatic friction between the two countries.
Italy insists the marines should be prosecuted in their home country because the shootings involved an Italian-flagged vessel in international waters, but India says the killings took place in waters under its jurisdiction.
Rome has said Massimiliano Latorre and Salvatore Girone will not go back to India in view of the "formal international controversy" between the two countries.
New Delhi's demand comes amid anger over Rome's decision, as politicians from the opposition Bharatiya Janata Party (BJP) accused Italy of treating India like a "banana republic".
"This is contempt of the Supreme Court of India. Is India a banana republic? How can the Italians treat India like this?" BJP spokesman Prakash Javadekar told AFP.
The marines were granted special permission once before to return home to Italy for Christmas, but later returned to India.
Armed guards are increasingly deployed on cargo ships and tankers in the Indian Ocean to tackle the threat posed by Somali pirates, who often hold ships and crews hostage for months demanding multi-million-dollar ransoms.