Javier Milei has condemned the UN as he warned that Argentina would take “matters into our own hands” in its dispute with Britain over the sovereignty of the Falkland Islands.

In a caustic speech at the general assembly in New York, the Argentinian president criticised the UN for being ineffective when it came to the long-running tensions over the British overseas territory in the south Atlantic known in Argentina as the Malvinas.

“An organisation that set out to defend the territorial sovereignty of its members decided to look the other way regarding the situation of the Falkland Islands,” Milei said of the UN, adding that Argentina was willing to act unilaterally over recent oil exploration near the territory.

The president criticised the Sea Lion project, a major offshore oil development located in the North Falkland Basin, describing exploitation of the territory’s resources as an “unlawful act”.

The president told the assembly that Argentina would “not remain indifferent to those who exploit resources under illegal foreign occupation”.

“Argentina is not going to sit around waiting for the UN and the international community to live up to their own mandate,” he said. “We’re going to take matters into our own hands.”

Argentina has accused the UK of flouting a 1976 UN resolution ordering both parties to desist from unilateral action on the islands. Milei’s government began sanctions proceedings this month against more than 60 companies and people linked to the oil drilling project.

The Falkland Islands government had approved the field development and production plans for the project, which is a joint venture between an Israel-based energy company and a London-listed oil and gas exploration company.

The UN does not officially recognise either British or Argentine sovereignty and maintains that the archipelago’s status remains a disputed matter that must be resolved through bilateral negotiations. It has repeatedly invited both governments to find a peaceful solution to the dispute that erupted into conflict in 1982 after an invasion by Argentinian forces.

The 74-day conflict ended with the surrender of the Argentine forces. It cost the lives of 649 Argentine military personnel, 255 British military personnel and 3 Falkland Islanders.

“For us, the Malvinas are a national cause,” Milei told the general assembly. The UN, he said, was a “useless organisation whose only purpose is to sustain a cast of faintly arrogant parasites masquerading as well-intentioned bureaucrats”.

“That’s why the Malvinas are not merely an issue between Argentina and the United Kingdom,” he said. “They also raise a question regarding the ability of this organisation to enforce its own resolutions.”

A referendum on the political status of the archipelago was held in the Falkland Islands in 2013. On a turnout of 92%, 99.8% voted to remain a British territory, with only three votes against.

Milei told the UN delegates that the principle of self-determination should not apply for the Falkland Islands as “the population was implanted by the occupying power on a territory whose sovereignty is in dispute”. “We call on the United Kingdom to resume negotiations with a view to finding a peaceful solution to the sovereignty dispute as required by international law,” he said.

Last month, Donald Trump said he was ​reviewing the US’s neutral position on ​the Falklands. The issue was a topic of discussion this week in a first meeting between Trump and the UK’s prime minister, Andy Burnham.

“The ‌clear ⁠position is: we will stand firm in the face of any threats,” Burnham said. “We will defend the ​right of ​the ⁠Falkland Islanders to self-determination and to remain British. I just ​wanted ⁠the president to know directly from me, that’s the clear British ⁠position, ​and he very ​much understood what I was saying.”