Responding to the issue raised by the Opposition in both Houses of Parliament, Dr Singh noted that the country is agitated over Italy's action, which is unacceptable, and said the government will pursue all diplomatic channels to bring the two marines back.
Urging the Italian authorities to respect the undertaking given to the Supreme Court, he said they should return the two accused -- Massimiliano Latorre and Salvatore Girone -- to stand trial in India.
"They have violated every rule of diplomatic discourse and called into question solemn commitments given by an accredited representative of a government," Dr Singh said in the Lok Sabha, which witnessed uproar during Question Hour as well as Zero Hour.
The prime minister, who made a similar statement in the Rajya Sabha, said the government has already made it clear that this action by the Italian government is "not acceptable".
"If they do not keep their word, there will be consequences for our relations with Italy," Dr Singh said firmly, adding that a bilateral relationship has to function on the basis of trust.
Assuring Parliament that the government would continue to urge Italy through diplomatic channels to send back the marines, he urged the members to act and speak together, while dealing with the matter with the seriousness that it deserves.
The prime minister's response came after former external affairs minister Jaswant Singh and Communist Party of India -- Marxist leader Basudeb Acharia attacked the government on the issue, with the Bharatiya Janata Party leader dubbing the action of the Italian government as a "very curious Italian job".
Rajya Sabha also witnessed an uproar over the issue, with demands for the arrest of Italian Ambassador Daniele Mancini.
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