Argentine President Javier Milei escalated his country's dispute with Britain over the Falkland Islands on Thursday, vowing new measures to halt an oil project near the British-controlled archipelago and praising U.S. President Donald Trump for saying Washington could reconsider its neutral stance on the islands' sovereignty.

Milei framed Trump's comments as proof that his close relationship with the U.S. president — which political opponents have criticized as overly deferential — was delivering results.

"The United States is considering this change in position because it knows that Argentina has a reliable partner, aligned with Western values, in a strategically important position that can be a valuable ally in the decades to come," Milei said in a nationally televised speech.

The Argentine leader then announced sweeping actions aimed at halting development of the deep-sea Sea Lion oil project, located roughly 220 kilometers (140 miles) north of the islands, where British company Rockhopper Exploration and Israel's Navitas Petroleum plan to begin drilling in the coming months and start pumping oil in 2028. Argentina regards the project as an illegal exploitation of resources in waters it claims as its own.

Sea Lion, discovered by Rockhopper in 2010, has been delayed for years by funding gaps, low oil prices and licensing disputes, and Navitas joined the project in 2022 — meaning the first Falklands oilfield has been more than a decade in the making. What to watch next is whether Milei's threatened sanctions, which would need to pass through Argentina's Congress, are enacted into law and whether any foreign operators or investors respond by scaling back involvement, as Argentina has targeted Falklands-linked shipping and energy firms with boycotts and penalties in past rounds of the dispute.

He threatened tougher sanctions against companies involved in the offshore drilling and announced new funding for a naval base in Argentina's southernmost province of Tierra del Fuego, intended to strengthen the country's military presence near the islands, known in Argentina as the Malvinas.

"Argentina will not stand idly by," Milei said. "Any further advance on the Malvinas Islands will be considered a violation of our national security."

U.K. Defense Secretary Wes Streeting responded that Britain's commitment to the Falkland Islands was "unshakeable."

"Milei's statement overnight tells us more about domestic politics in Argentina than it does about the Falkland Islands," Streeting wrote on X.

Milei's effort to refocus attention on the Falklands marks a striking turn for a leader who has faced criticism at home for warming ties with Britain and expressing admiration for Margaret Thatcher, the British prime minister reviled in Argentina for leading the campaign to retake the archipelago during the 1982 Falklands War.

That two-month conflict, which killed 649 Argentine troops, 255 British service members and three islanders, remains a sore point in Argentina more than four decades later.

The sovereignty claim is enshrined in Argentina's constitution and is frequently invoked as an expression of national identity, from banknotes to World Cup soccer chants. It is also one of the few causes that cuts across the country's stark political divides, giving Milei — who faces reelection next year — a welcome political opening as his approval ratings slip and the economy sputters.

"We can argue about my style. We can disagree over fiscal or exchange-rate policy," Milei said. "But there are causes that rise above any political difference. The Malvinas is one of them."

Some observers were skeptical.

"He wants to use the legitimate sovereignty claim over the Malvinas Islands to regain ground ahead of the election year and serve U.S. interests in its dispute with Britain," said Nicolás del Caño, a leftist opposition lawmaker.

Argentina maintains that it inherited sovereignty over the islands from its former colonizer, Spain, and that Britain has illegally occupied them since 1833. Britain rejects that claim, citing the islanders' desire to remain a British overseas territory.

For decades, successive U.S. administrations have remained neutral on the competing claims while recognizing Britain's de facto administration of the islands. Any departure from that position would represent a major diplomatic affront and inflame already high trans-Atlantic tensions.

On Monday, Trump stirred concern in Britain when asked whether his administration was reviewing its stance on the decades-old dispute. "I always review every position," he replied. "That's just one of many."

Then, in an interview aired Thursday with British broadcaster GB News, Trump avoided directly answering a question about whether the U.S. would "come to the aid" of Britain in another conflict over the Falklands. Instead, he repeated past complaints that Britain had not provided sufficient support for the U.S.-led bombing campaign against Iran.

"Your country was not there to help me," Trump said, recalling that Britain's former prime minister, Keir Starmer, had told him the country did not have ships to contribute to the campaign. "It was pretty sad, the whole thing."

The Trump administration has floated the Falklands as leverage before: an internal Pentagon email leaked in April first raised the prospect of Washington reconsidering its position on the islands as one possible way to punish NATO allies that declined to join the U.S. war on Iran.

Trump's comments prompted Downing Street to insist that Britain would not yield sovereignty over the Falklands.

"Sovereignty rests with the U.K., and the islanders' right to self-determination is paramount," said Tom Wells, spokesman for British Prime Minister Andy Burnham, speaking earlier this week. He pointed to a 2013 referendum in which the roughly 4,000 residents of the Falkland Islands voted overwhelmingly in favor of remaining a British overseas territory.

Under pressure from Argentina's populist opposition, which accuses him of neglecting the country's sovereignty claim, Milei has grown more vocal on the Falklands as plans for large-scale oil production around the islands raise the economic stakes of the dispute.

In his speech, Milei warned that the Sea Lion project could trigger a broader Falklands oil boom, enriching the islands with resources Argentina claims as its own and further entrenching Britain's presence.

"If we allow it, we will be creating an incentive for the British government to deepen the occupation of the islands and the exploitation of our resources," Milei said.

He vowed to fast-track sanctions against companies involved in oil projects around the islands and to extend penalties to suppliers, shareholders and directors. His proposed legislation could also bar companies tied to such projects from operating or signing contracts in Argentina.

Despite slashing public spending elsewhere as part of his austerity drive, Milei also pledged additional money to build a naval base in Tierra del Fuego and upgrade Argentina's telecommunications capabilities there, strengthening the country's presence in the South Atlantic.

"A poor country without armed forces can hardly make effective progress on its sovereignty claims," he said.

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Associated Press writers Jill Lawless in London, Zeke Miller in Washington and Almudena Calatrava in Buenos Aires, Argentina, contributed to this report.

This story was originally featured on Fortune.com.