MONTEVIDEO (AFP) - Uruguay's President Jose Mujica was left red-faced on Thursday after disparaging remarks apparently aimed at Argentine counterpart Cristina Kirchner and her late husband were picked up by an open microphone.
Buenos Aires swiftly responded with an official protest, calling the comments "unacceptable".
"This old hag is worse than the cross-eyed man," Mr Mujica was caught saying at the start of a news conference while speaking quietly with another official.
El Observador newspaper, which posted the audio on its website, said Mr Mujica was referencing the Kirchners and did not realise that the microphones were already on.
Mr Nestor Kirchner died suddenly of a heart attack in 2010 and had a lazy eye.
Word of the slip-up shut down the paper's website, which recorded historic traffic, according to the outlet's digital content manager.
The comment also quickly gained traction on social media.
An hour later, Mr Mujica told the online version of La Republica newspaper that he had not talked about Argentina and was not going to clarify anything.
But Argentine Foreign Minister Hector Timerman slammed the remarks as "unacceptable" and "denigrating", adding that they offended the memory of the deceased.
An official protest was delivered in the form of a note to Uruguay's ambassador to Argentina, Guillermo Pomi.
Mr Mujica, 77, is a former guerilla who took office in 2010. Mr Nestor Kirchner was Argentina's president from 2003 to 2007. His wife Cristina succeeded him and won re-election in 2011.