In a strongly-worded statement in both Houses of Parliament, where government came under attack on the issue, Singh accused Italy of "violating every rule of diplomatic discourse" and termed as "unacceptable" its decision not to send back the accused marines Massimiliano Lattore and Salvatore Girone.
The two marines were permitted by the Supreme Court on February 22 to go to Italy for four weeks to cast their votes in general elections following a written assurance by Italian Ambassador Daniele Mancini that they will return by March 22. There are also demands that the Ambassador be expelled from the country.
"If they do not keep their word there will be consequences for our relations with Italy," Singh said firmly, adding that bilateral relationship has to function on the basis of trust.
While the Prime Minister promised that the government will pursue through diplomatic channels the efforts to bring the marines back to India, Mancini insisted his country has not gone back on its assurance to the Supreme Court.
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The Ambassador, however, argued that Italy was not going back on the assurance.
Asked if the Italian Ambassador will be given marching orders in view of breach of assurance by him, Foreign Secretary Ranjan Mathai said,"I think we have made our position very clear....We are awaiting their response. As soon as the response is received, we will take a decision on what to do."
The two marines are charged with homicide for killing two fishermen off the Kerala coast in February last year in an anti-piracy operation.