Felipe Calderon: document to give Argentina "unanimous support"
Latin American and Caribbean leaders have backed Argentina's claim over the Falklands, Argentine President Cristina Fernandez de Kirchner has said.
At a regional summit in Cancun, Mexico, a document has reportedly been drafted giving Argentina unanimous support.
It comes a day after a British oil company began drilling for oil off the islands, a move Argentina objected to.
The UK's defence minister said the government would take whatever steps necessary to protect the Falklands.
Argentina and Britain went to war over the South Atlantic islands in 1982, after Buenos Aires invaded the archipelago.
The conflict ended with UK forces wresting back control of the islands, held by Britain since 1833.
Hugo Chavez: "Queen of England, the empires are over" - footage courtesy of VTV
No official statement has been made in Cancun, but Mexican President Felipe Calderon reportedly said a document had been drawn up offering Buenos Aires full support in its territorial dispute with London.
The Argentine president accused the British government of ignoring international law by allowing a British oil exploration company to begin drilling near the islands.
She said: "I think the important thing is that we have achieved very strong support, something that legitimates our claims fundamentally against the new petroleum activity."
The BBC's Andy Gallacher in Cancun says that any broad agreement at the summit could put more pressure on the British government in what has become an escalating diplomatic row.
'Return the Malvinas'
Venezuelan President Hugo Chavez reiterated his support for Argentina.
The Ocean Guardian is in Falkland Islands waters
"We demand, and I think all of us should do the same, the withdrawal of the submarine platform, and that the English government... give that land back," he said.
Before leaving for the summit, Nicaraguan President Daniel Ortega called for "Britain to return the territory of the Malvinas to its real owners - to return it to Argentina" on Venezuelan Telesur television.
Leaders at the summit, between the Rio Group and the Caribbean Community (Caricom), have also discussed plans for a new pan-American alliance which would exclude Canada and the United States.
The new grouping would serve as an alternative to the Organisation of American States, the main forum for regional affairs in the past 50 years.
The British-contracted rig Ocean Guardian began drilling 100km (62 miles) north of the Falklands on Monday, despite fierce opposition from Argentina.
Desire Petroleum, which is overseeing the operation, said drilling had started on the Liz 14/19-A exploration well at 1415 GMT.
Argentina claims sovereignty over what it calls the Islas Malvinas and has imposed shipping restrictions.
But UK Defence Minister Bill Rammell said the government had a "legitimate right" to build an oil industry in its waters.
Mr Rammell said the UK would take "whatever steps necessary" to protect the islands and that it had made Argentina "aware of that".
Argentina has ruled out military action and is trying to pressure Britain into negotiations on sovereignty.
During the seven-week war in 1982 over the Falklands, 649 Argentine and 255 British service personnel were killed.
Last year Argentina submitted a claim to the United Nations for a vast expanse of ocean, based on research into the extent of the continental shelf, stretching to the Antarctic and including the island chains governed by the UK.
It is due to raise the issue at the UN later this week.
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