Venezuelan President Hugo Chavez has attacked US counterpart George W Bush as a "symbol of domination" as the pair continue rival Latin American tours.
Protesters took to the streets ahead of Mr Bush's arrival in Montevideo
Speaking at an "anti-imperialist rally" in Buenos Aires, Mr Chavez said Mr Bush was no more than a "political corpse".
Mr Bush arrived in the capital of neighbouring Uruguay, Montevideo, as Mr Chavez addressed the crowd of 40,000.
It is as close as the two rivals will come, separated by just 65km (40 miles) across the River Plate.
'Gringo go home!'
Mr Chavez, dressed in his trademark red shirt, shouted to the crowds: "The little imperial gentleman from the north must be across the river by now. Let's send him a big shout: Gringo go home!"
Before leaving Brazil, where the US president signed a deal aimed at promoting the bio fuel ethanol as an alternative to petrol, Mr Bush said his trip was aimed at promoting neighbourly relations.
"My trip is to explain as clearly as I can that our nation is generous and compassionate," Mr Bush said before heading for the second stop in his five-nation tour, Uruguay.
But protests before his arrival in the capital, Montevideo, ended with demonstrators smashing the windows of two McDonald's stores.
In Brazil on Thursday, about 20 were injured as demonstrations against Mr Bush erupted into clashes on the city's main avenue.
Hearts and minds
Mr Chavez insists that the timing of his tour is purely coincidental but the BBC's Daniel Schweimler in Buenos Aires says the pair are embroiled in a battle for hearts and minds in Latin America.
Both presidents are trying to garner public support in Latin America
Many analysts say the US president's tour is an attempt to counter the growing influence of his leftist arch-rival.
Mr Bush is visiting Brazil, Uruguay, Colombia, Guatemala and Mexico while Mr Chavez will move on from Argentina to Bolivia.
The Venezuelan president has a number of close allies in the region - most notably the leaders of Bolivia and Ecuador.
Others such as Argentine President Nestor Kirchner, our correspondent says, cannot afford not to be friends with Mr Chavez, who enjoys massive support across Latin America, especially among the millions of poor.