The secretary of the Treasury, Scott Bessent, says “all options for stabilization” are on the table for Argentina as one of MAGA world’s favorite Latin American leaders faces the first serious financial crisis of his two-year tenure.

President Javier Milei — a self-described “anarcho-capitalist” who sailed into office on a populist platform of economic reform — has been working to curb runaway inflation and restore growth since winning a landslide election in 2023 but his party lacks a working majority in the Argentine congress. Mr. Milei has promised to lower taxes, cut government budgets, and end stifling regulation that has hindered economic expansion.

The International Monetary Fund says Mr. Milei’s policies have started to work to undo years of left-wing Peronism. Inflation has dropped from more than 200 percent to 35 percent, the lowest in five years, and IMF projections have it falling to below 10 percent in the coming years.

But the South American country faces a market selloff of its peso currency and asset prices since the opposition party won local elections at the Buenos Aires province last month. Those wins have unnerved investors. Argentina holds a wider midterm election in October.

The Argentinian senate also recently passed bills to hike government spending on several big programs, a threat that could derail Mr. Milei’s austerity push.

In a series of X posts on Monday, Mr. Bessent says the South American country is a “systemically important US ally” and the United States backs Mr. Milei’s reforms.

Mr. Bessent says the United States Treasury is considering currency swap lines — with American dollars being used to lend to Argentinian banks, direct currency purchases, and purchases of dollar-denominated government debt from the Treasury’s exchange stabilization fund. He adds that other options could also be considered.

“Support for fiscal discipline and pro-growth reforms are necessary to break Argentina’s long history of decline,” he says.

Mr. Bessent says that opportunities for private investment remain strong in Argentina and confirmed that he and President Trump will meet with Mr. Milei at New York on Tuesday and more details will be available a short time after that.

Argentina’s Merval stock index jumped nearly 10 percent after Mr. Bessent’s announcement, but remains down for the year.

In another move on Monday, the Milei administration announced a temporary suspension of Argentina’s taxes on grain exports to encourage the flow of export dollars into the country, the Financial Times reported.