NEW DELHI: Angry politicians attacked the government Tuesday for allowing two Italian marines accused of killing a pair of Indian fishermen last year to leave the country - a case that has caused a huge uproar in India.

The government allowed the marines to return to Italy in February to vote in national elections and to celebrate Easter with their families. Italy announced Monday it would not send the marines back to India to face trial as had been expected.

Opposition lawmakers protested in both houses of India's Parliament demanding the government explain what it plans to do to bring the marines back.

India said it is considering what steps to take next in the international dispute and is exploring the legal and diplomatic options it can pursue.

Minister for External Affairs Salman Khurshid said the government would respond appropriately to a letter from the Italian government saying the marines would not return to India.

"We are studying the implications of the position taken by Italy. We will take an informed decision after examining the communication from Italy," Khurshid said.

But opposition political parties said the decision showed Italy did not take the Indian government seriously.

"This is a betrayal by the Italian government," said Rajiv Pratap Rudy, spokesman of the main opposition Bharatiya Janata Party. "It is a breach of trust between two sovereign nations and the act is completely unacceptable."

Rudy said the government should make all out efforts to bring the marines back to face "trial under Indian laws and in Indian courts."

The marines, Massimilian Latorre and Salvatore Girone, were part of a military security team aboard a cargo ship when they opened fire on a fishing boat in February last year that they said they mistook for a pirate craft, killing the two fishermen. The shooting took place off the coast of India's southern state of Kerala.

On Tuesday, lawmakers from Kerala met with Prime Minister Manmohan Singh to urge him to ensure justice for the families of the fishermen.

P.C. Chacko, a Congress Party lawmaker who was present at the meeting, said Singh assured them that India's foreign ministry would pursue the case with Italian authorities and "use all diplomatic channels to bring them back."

The wife of one of the slain fishermen said the decision to let the marines go home to vote appeared to be part of a plan to spare them from facing trial.

"This is nothing but a conspiracy at the highest level," said the wife, Dora Valantine. "The Indian government should ensure that they bring back the two and make them stand trial in this country."

Last year, Italy paid compensation of 10 million rupees ($192,308) each to the families of the fishermen.

The marines said they had put their faith in the Italian government to help them out.

"I knew that our government wasn't abandoning us. It wouldn't abandon us. They gave us four weeks from when we returned to Italy to vote, and I felt that something would happen, something positive, I mean," Girone was quoted as saying by the Milan daily Corriere della Sera.

But he said they were not celebrating their release.

"'There isn't anything to celebrate. Our case is not over yet," Girone said.

The incident sparked a diplomatic dispute between the countries. Italy maintains the shooting occurred in international waters and that Rome should have jurisdiction. India says the ship was in Indian territorial waters.

The Indian Supreme Court ruled earlier this year that the men should be tried by a special court to be set up by the central government in consultation with the chief justice. The decision removed the case from the jurisdiction of the southern state of Kerala.

The Indian government had earlier allowed the marines to go home over the Christmas holidays, after which they returned to India.

In February, India's Supreme Court allowed them to return home to vote after the Italian ambassador to India gave a guarantee that the marines would be back.

The Italian government came under attack in that country's media on Tuesday.

The Rome daily La Repubblica said the move by Premier Mario Monti's caretaker government "dealt a terrible blow to our credibility from the point of view of international image."

The newspaper said the decision made the fishermen victims twice. "First by the tragic misunderstanding, then by a fraudulent behavior on the part of a country that should in any case take responsibility for what happened."

Italy said Monday that India's decision to try the marines would violate their rights, in particular the principle of immunity for foreign state actors, and they would not go back.