Buenos Aires, Argentina - Argentina's opposition on Monday criticized a visit by US lawmakers to the southernmost city of Ushuaia, at the gateway to the Antarctic, seeing it as sign of Washington's potential interests in the region.

The unannounced arrival of an American government aircraft in the capital of Tierra del Fuego province fueled suspicions that President Javier Milei, a close ally of counterpart Donald Trump, is seeking to establish a joint naval base with the US in the area.

The US embassy in Buenos Aires confirmed the plane was carrying a bipartisan delegation from the House Committee on Energy and Commerce, but did not name the members.

According to local media, the Congress members traveled to the city in Patagonia region on a US Air Force Boeing C-40 Clipper.

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The embassy said they met with government officials and key stakeholders to discuss environmental degradation, permits for mine and waste management, the processing of critical minerals, public health, and medical safety.

Emiliano Fossatto, legal secretary of Tierra del Fuego province which is governed by the left-wing opposition, told Radio 10 that the visit generated substantial "uncertainty" and that there had been no prior or subsequent communication with local authorities.

"The geolocation of the port of Ushuaia is significant; it's the gateway to Antarctica... a commercial and tourist waterway, so there may certainly be other motives" behind the visit, Fossatto added.

Senator Cristina Lopez, also an opponent of Milei, on X demanded explanations from the government over the delegation's arrival.

"Tierra del Fuego is not a foreign military base," she declared.

Milei, in power since December 2023, has already received two heads of the US Southern Command in Ushuaia: Laura Richardson in 2024 and Alvin Holsey last year.

Both visited the Integrated Naval Base project, which Argentina has been building since 2022.

Milei's government has denied that Washington is involved in the conception of the base.

Richardson also visited Argentina during the presidency of Milei's left-wing predecessor, Alberto Fernandez.