David Cameron has upbraided the Argentinian foreign minister for raising the Falklands over dinner at a Brussels summit.
Hector Timerman pushed the issue of who owns the islands during discussions between Community of Latin American States (CELAC) representatives and EU leaders.
According to Argentinian media, he said: “The Argentine government expects countries from the European Union to support the United States resolution that urges Argentina and the UK to dialogue over the Malvinas Islands.
“One hundred and eighty-two years ago, the United Kingdom expelled Argentine population and authorities from the islands, breaking the territorial integrity of my country."
A senior Downing Street source said Mr Cameron demanded to be allowed to respond even though he was not due to speak next. The Prime Minister pointed to the recent Falklands referendum on whether they wanted to retain links to the UK and insisted "everyone has the right to self-determination".
He also argued that it was "totally inappropriate" for Argentina to be "threatening" investors in the area, the source said.
A No 10 spokeswoman said: "At the dinner, the Prime Minister robustly defended the Falklands and the islanders' right to self-determination in response to the Argentine foreign minister raising the issue.
"The Prime Minister underlined that the islanders had expressed their view in a referendum and that should be respected.
"He went on to add that the waters around the Falklands were territorial waters and it was unacceptable of Argentina to threaten investors seeking to operate there."