The summit intended to promote unity among Latin American leaders
Venezuelan President Hugo Chavez and Colombian President Alvaro Uribe have clashed at a Latin American summit on Monday, officials say.
Mr Uribe urged Mr Chavez to "be a man!", while Mr Chavez told his Colombian counterpart to "go to hell!".
The altercation took place on the sidelines of a two-day summit in Mexico to unite Latin American countries.
Cuban leader Raul Castro and summit host Mexico's Felipe Calderon attempted to reconcile the two, reports say.
The row at a private meeting started after Mr Uribe complained to Mr Chavez about the Venezuelan trade embargo on Colombia, upsetting the Venezuelan president.
Be a man! These issues are meant to be discussed in these forums. You're brave speaking at a distance, but a coward when it comes to talking face to face.
Mr Chavez then accused Mr Uribe of planning his assassination by a paramilitary squad and threatened to walk out of the summit.
At this point, Mr Uribe is said to have shouted at Mr Chavez: "Be a man! These issues are meant to be discussed in these forums. You're brave speaking at a distance, but a coward when it comes to talking face to face."
There have been growing tensions between the two countries after the signing of a military agreement between Colombia and the US last year, while Mr Chavez has been an outspoken critic of the US in Latin America.
Mr Calderon later told reporters that Venezuela and Colombia must settle their differences in "respectful dialogue... to avoid accusations and recriminations".