(By Denis Greenan). Rome, March 19 - The European Union on Tuesday backed Italy in a diplomatic row with India over the alleged murder by two marines of two Italian fishermen last year. But the leader of India's ruling Congress party, Italian-born Sonia Gandhi, voiced continued anger over Italy's decision not to send the marines back, saying "no country can take India for granted". Catherine Ashton, the European Union's high representative for foreign affairs, said Tuesday that India was violating the Vienna Convention on diplomatic relations after India's Supreme Court ordered Italy's ambassador to New Delhi not to leave the country. The court imposed the order on Ambassador Daniele Mancini after Rome said marines Massimilano Latorre and Salvatore Girone would not return to India after being allowed to come home last month to vote in Italy's general election. Latorre and Girone are charged with shooting and killing on February 15 last year Indian fishermen Jelestine Valentine and Ajesh Binki from the oil tanker Enrica Lexie, which they were guarding against pirates. In her statement, Ashton said that: "the 1961 Vienna Convention on Diplomatic relations is a cornerstone of the international legal order and should be respected at all times. "Any limitations to the freedom of movement of the Ambassador of Italy to India would be contrary to the international obligations established under this Convention". Up to now the EU had seemed to be trying to distance itself from an increasingly acrimonious row, saying it was a bilateral dispute. Ashton expressed "concern" about the Indian Supreme Court's March 14 decision to impose the ban on Mancini leaving India and the March 18 decision to extend it until it next hears the case on April 2. The Vienna Convention states that the rights of diplomats are "inviolable" and they cannot be detained. However, the Indian Supreme Court said Mancini's case is an exception, arguing that, on the basis of Article 32 of the Vienna Convention, he "automatically lost" his diplomatic immunity by signing a guarantee that the marines would return. Rome, which has declared the travel ban "illegal", has always denied that India has jurisdiction over the marines case, saying the incident took place in international waters. Italian Foreign Minister Giulio Terzi said last week that the decision to not return the pair was legitimate and Italy had a strong case which it wanted to put to independent arbitration. An earlier deal, which allowed the marines to return to Italy for Christmas, was respected by both governments and was seen as a positive step - as well as a sign of goodwill - towards a diplomatic solution. "The High Representative continues to hope that a mutually acceptable solution can be found through dialogue and in respect of international rules and encourages the parties to explore all avenues to that effect," read Ashton's statement. Meanwhile, in New Delhi, the president of the ruling Indian National Congress, Sonia Gandhi, described as "unacceptable" Rome's decision not to return the marines. She warned that "no country can take India for granted". Speaking to senior Congress party figures, the Italo-Indian president said India should do "everything possible" to bring back Latorre and Girone. "The defiance of the Italian government on the question of the two marines and its betrayal of a commitment to our Supreme Court is outright unacceptable," Gandhi said. "All means must be pursued to ensure that the commitment made by the Italian government to our Supreme Court is honoured".