Argentina has made an official protest after the Uruguayan president was caught on microphone apparently referring to President Cristina Fernandez de Kirchner as an “old hag”.
President Jose Mujica was overheard saying: “This old hag is even worse than the cross-eyed man.”
A Uruguayan newspaper has posted audio of his comments on its website.
It has claimed that he was referring to Ms Fernandez and her late husband, who she succeeded as president.
Ms Fernandez’s husband, Nestor Kirchner, had a lazy eye. He died suddenly of a heart attack in 2010.
President Mujica has denied that he had been talking about the Kirchners, but has so far failed to explain who else he was referring to.
In a weekly radio address on Friday, he made no apology for his earlier remarks but spoke of the two countries as being born “from the same placenta of the Argentine peoples”. “No-one and nothing can separate us,” he said.
Frequent clashes
He made the controversial comments at the start of a news conference while speaking quietly with another official.
El Observador newspaper posted the audio on its website, claiming that the president did not realise that the microphones were on.
The newspaper said that its website has crashed because of historically high levels of traffic generated by its coverage of the incident which has also gained the attention of social media.
Argentine Foreign Minister Hector Timerman summoned the Uruguayan ambassador in Buenos Aires, Guillermo Pomi, to protest about the comments.
“It is unacceptable that derogatory comments that offend the memory… of a deceased person, who cannot defend himself, have been made, particularly by someone to whom Nestor Kirchner considered his friend,” a statement issued by the foreign ministry said.
Correspondents say that President Mujica, 77, a former guerrilla leader who took office in 2010, has clashed in the past both with Ms Fernandez and Nestor Kirchner.
Relations between Uruguay and Argentina have recently been strained because of concern in Montevideo over what it sees as protectionist measures enforced by Buenos Aires.
Nestor Kirchner was Argentina’s president from 2003 to 2007. His wife Cristina succeeded him and won re-election in 2011.