Days after Donald Trump declined to rule out changing Washington's stance on the Falkland Islands, President Javier Milei used a televised address late on September 3 to harden Argentina's decades-old sovereignty claim over the territory, threatening sanctions on oil companies drilling nearby and promising new funds for a naval base in Tierra del Fuego.

Speaking from the Casa Rosada, the presidential palace in Buenos Aires, Milei said the Falklands, which Argentina calls the Malvinas, were "Argentinian, historically and legally" and that there was "no debate" over the matter. He said Argentina would not "stand idly by" and needed to "recover" the islands. Britain has held the territory since 1833, and the two nations went to war over it in 1982.

The Argentine leader singled out Sea Lion, an offshore development roughly 220km north of the Falklands led jointly by London-listed Rockhopper Exploration and Navitas Petroleum, headquartered in Israel, describing it as a "concrete and urgent danger" to national sovereignty. "If we do not act firmly and swiftly today, in a few months they will have the material capacity to seize the oil reserves that lie under our sea," he said.

Trump's remarks came in a GB News interview broadcast on September 3. Pressed on whether the US would support Britain militarily should the Falklands dispute turn violent again, he gave no assurance, instead repeating his complaint that London had offered little help for the US and Israeli-led bombing campaign against Iran. Earlier in the week, the US president had told reporters in the Oval Office that he was open to reconsidering "every position," including on the Falklands, although US officials have since maintained that Washington's neutral stance is unchanged.

Ed Miliband, the UK's foreign secretary, dismissed Milei's claim, calling Britain's commitment to the islands "unwavering" and arguing that international law guaranteed the islanders a say over their own future. Wes Streeting, the UK defence secretary, said Milei's statement "tells us more about domestic politics in Argentina than it does about the Falkland Islands," adding that the islands "are British because Falkland Islanders choose to be British."

Milei rejected that argument, saying the remote archipelago’s population, as residents of what he called "usurped territory," did not have "a legitimate right to self-determination" and that a 2013 referendum, in which 99.8% of islanders voted to remain British, was "invalid."

The libertarian leader also unveiled a decree requiring state agencies to flag suspected legal breaches in the islands directly to the foreign ministry, which would then have the power to penalise the companies and suppliers involved in oil and gas work there. Separately, he said his government would put a National Sovereignty Defence Bill before Congress, tightening existing sanctions law and setting up a new National Security Council. He also said he would sign an emergency decree to increase defence ministry funding for an integrated naval base in Tierra del Fuego, a project begun in 2022, which he said would become the "most important logistics hub in the South Atlantic."

Rockhopper and Navitas played down the impact of the threatened measures. In a joint statement, the companies said the episode was "not expected to have any material effect" on the Sea Lion timeline and that their licences, granted by the Falklands' local government, remained valid with the "full and continuous support" of the UK government.

Pablo Quirno, Argentina's foreign minister, said the presence of an Israeli company in the project would not damage relations with the Jewish state, one of Argentina's closest allies under Milei, adding that Navitas was already subject to Argentine sanctions. He said the measures announced on September 3 had been in preparation for six months. Milei declared himself "the most Zionist president in the world" earlier this year and takes pride in being a close ally of Israeli Prime Minister Benjamin Netanyahu.

Sea Lion, which lies at a depth of 450 metres, is targeting first oil in early 2028 with initial output of 55,000 barrels a day, against Argentina's national production of about 915,000 bpd. According to a public filing by Rockhopper reviewed by consultancy Netherland, Sewell & Associates, the project could generate between $2.85bn and $8.8bn for the Falklands government over roughly 40 years, based on a 9% royalty rate and 25% income tax.

The 1982 war between Britain and Argentina over the islands claimed the lives of 649 Argentine and 255 British service personnel. The dispute resurfaced in July when Argentina's football team displayed a banner reading "the Malvinas are Argentine" after eliminating England from the World Cup semi-finals.

Facing corruption allegations within his government and rising unemployment and poverty despite successfully curbing inflation, Milei is seeking re-election next year, and some analysts see his sudden prominence on the Falklands question as a way of shifting attention elsewhere. The president has long professed admiration for Margaret Thatcher, the UK Conservative prime minister who led Britain through the 1982 war, and only revived Argentina's sovereignty claim publicly in recent months, after word emerged that the White House might be rethinking its stance.

Milei cast Trump's openness to reviewing the US position as vindication of his close ideological alliance with the Trump administration. "The United States is considering this change in position because it knows that in Argentina, it has a reliable partner, one aligned with Western values, in a position of strategic importance," he said.