* Dispute over killing of fishermen escalates
* Charged Italian marines failed to return to India
* India top court barred Italian envoy from leaving country
BRUSSELS, March 19 (Reuters) - India would be breaking international law if it stops Italy's ambassador from leaving the country in a dispute over two Italian marines charged with killing two Indian fishermen, the European Union said on Tuesday.
The statement was the bloc's most forceful intervention yet in the festering dispute over the marines which has soured relations between India and EU member Italy.
India's top court last week temporarily barred the envoy, Daniele Mancini, from leaving after Rome refused to send the marines back to India to face trial following a home visit.
The marines Massimiliano Latorre and Salvatore Girone, part of a security team protecting a tanker from pirates, are accused of shooting the two Indian fishermen off the coast of Kerala in February last year.
EU foreign policy chief Catherine Ashton noted the Indian court's ruling about the ambassador "with concern", Ashton's spokesman said.
Ashton regarded the 1961 Vienna Convention, which sets rules for diplomatic relations, as a cornerstone of the international legal order that should be respected at all times, he said in a statement.
"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," he added.
"(Ashton) 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," the statement said.
The EU statement echoed comments by Italy's Foreign Ministry on Monday that the Indian court's decision violated diplomatic immunity law.
India's Supreme Court had allowed the marines to go home for four weeks to vote in last month's parliamentary election, provided they returned.
They have not done so, and Italy's Foreign Ministry said the incident had become a formal dispute over U.N. laws.
India's Supreme Court said in a long-awaited ruling in January that India had jurisdiction to try the marines, but Italy has challenged that decision, arguing that the shooting took place in international waters.
Italy's announcement that the sailors would not return caused an uproar in India' parliament and Prime Minister Manmohan Singh's government is under pressure to respond forcefully. (Reporting by Adrian Croft; Editing by Andrew Heavens)