Argentine President Javier Milei used a televised national address Thursday night to revive his country's decades-old claim to the Falkland Islands, vowing tough new sanctions against oil companies drilling near the British-held archipelago just as U.S. President Donald Trump cast doubt on whether Washington would back London in a future standoff.

"The Falkland Islands are Argentinian, historically and legally," Milei told viewers, describing offshore drilling near the islands as a "concrete and urgent danger" and pledging urgent legislation to punish firms operating there without Buenos Aires' approval, according to Al Jazeera.

The target is the Sea Lion project, a deep-water oilfield roughly 140 miles north of the islands being developed by Britain's Rockhopper Exploration alongside Israel's Navitas Petroleum, with drilling expected to begin this year and production slated for 2028. Milei said the sanctions would reach beyond the two companies to their suppliers, shareholders and directors, and that violators could be barred from operating in Argentina altogether. He also announced fresh funding for a naval base in Tierra del Fuego, near the South Atlantic islands.

Trump muddies the waters

The threat lands with extra force because of Trump. In an interview with GB News, the U.S. president declined to commit to backing Britain if Argentina moved on the islands, calling them "a long way away" and grumbling that London had offered only limited help with recent U.S.-Iran operations, according to CNN. It's a striking shift for a close Milei ally whose administration has otherwise courted Argentina as a regional partner.

Britain, whose forces defeated Argentina in the 10-week Falklands War of 1982 that killed more than 900 people, was quick to push back. Foreign Secretary Ed Miliband wrote that the UK's position "is unwavering," adding that the islands "are British and will remain so because that is the overwhelming position of the Islanders," whose right to self-determination he called "paramount" and "grounded in international law."

"The Falkland Islands are Argentinian, historically and legally." — Javier Milei

A 2013 referendum on the islands found 99.8% of Falklanders voting to remain a British Overseas Territory, a result London has repeatedly cited as settling the sovereignty question. Milei, whose approval ratings have slid amid painful austerity measures, has faced accusations from critics that he is leaning on the flag-waving cause to shore up domestic support.

Downing Street has so far signaled it will not escalate its diplomatic response, according to CNBC, even as Argentina's Congress prepares to take up Milei's proposed sanctions legislation in the coming weeks. Rockhopper and Navitas have not indicated any change to their Sea Lion drilling timeline. With Trump's remarks reopening questions about the durability of the U.S.-UK alliance in the South Atlantic, the dispute is likely to keep simmering well beyond Buenos Aires and London.