(recasts with Argentine response)
LONDON/BUENOS AIRES, April 9 (Reuters) - Argentina said it would begin legal action on Thursday against British energy firms operating near the Falkland Islands, in a growing war of words over the disputed South Atlantic territory.
The move is the latest diplomatic spat between Britain and Argentina, who fought a short war over the Falklands in 1982, and has led to both countries summoning the other's ambassador for a dressing down.
Last week, British firms Premier Oil Plc and Falkland Oil and Gas Ltd said they had made an oil and gas discovery at a well off the south Atlantic islands, the first in a nine-month drilling campaign.
Argentina's President Cristina Fernandez called the announcement "almost provocative", and Argentine officials warned they were planning legal action against British energy firms exploring off the shores of the Falklands, which lie 300 miles off the Argentine coast and 8,000 miles from Britain.
The two companies declined to comment about any legal action on Thursday.
In a further development, Argentina has also demanded answers over media reports Britain had spied on Argentine military and political leaders from 2006 to 2011, based on intelligence documents provided by the U.S. whistle-blower Edward Snowden.
After summoning Britain's ambassador over the alleged spying, Argentine Deputy Foreign Minister Eduardo Zuain told him legal action would begin against the British firms on Thursday.
Argentina's Ministry of Foreign Affairs said in a statement: "A lawsuit will be presented today against companies carrying out petroleum exploration activities on the Argentine continental shelf."
The discovery of oil has further raised tensions over control of the Atlantic archipelago more than 30 years after Argentine forces seized the islands and Britain sent a task force to retake them in a brief war which saw more than 600 Argentine and 255 British servicemen killed.
Britain said on Thursday it had summoned the Argentine ambassador to explain the threat to prosecute British energy firms.
"The UK has no doubt about its sovereignty over the Falkland Islands and surrounding maritime areas, nor about the Falkland Islanders' right to decide their own future," a British Foreign Office spokesman said.
"We object strongly to recent statements by the Argentine President and the Argentine ambassador to London and so summoned the ambassador to account for these."
Britain said last month it would reinforce its military presence on the Falklands to counter the "very live threat" posed by Argentina.
However, Fernandez, in a speech honouring soldiers who died in the failed 1982 invasion of islands, which Argentina calls Las Malvinas, dismissed the idea of Argentina being a threat. (Reporting by Michael Holden in London and Richard Lough in Buenos Aires; editing by Stephen Addison)