Venezuela's President Hugo Chavez has described his Mexican counterpart, Vicente Fox, as a puppy dog for United States imperialism.
Mr Chavez has become one of Washington's fiercest critics
Mr Chavez said Mr Fox had, as he put it, been left bleeding from last week's Summit of the Americas.
At the meeting, the US and Mexico were unable to win backing for a resumption of talks on a regional trade pact.
They faced opposition from five of the 34 countries attending, among them Venezuela and the host, Argentina.
The other 29 nations - including Mexico - said they wanted to resume talks on a Free Trade Area of the Americas (FTAA) in 2006.
Speaking before an audience of supporters and businessmen in the Venezuelan capital, Caracas, Mr Chavez said: "How sad that the president of a people like the Mexicans lets himself become the puppy dog of the empire."
The Mexican government has called in the Venezuelan Ambassador, Vladimir Villegas, for a meeting on Thursday to explain Mr Chavez's comments.
Earlier, Mexico and Argentina agreed to end their own row over the Summit of the Americas.
Mr Fox - a conservative who has been close to Washington on trade issues - had accused left-wing President Nestor Kirchner of being a poor host only interested in his domestic political support.
Mr Fox has been involved twice in verbal sparring
He said he was involved more with Argentines' image of the president than achieving a successful summit.
But Mr Kirchner replied: "Mr Fox should worry about Mexico and let me take care of Argentine matters".
The two countries' foreign ministries issued a joint statement on Wednesday attempting to calm the dispute, saying that their relations are "splendid".
Mr Chavez had great praise for his Argentine counterpart, who he said had wielded a sword of truth and reason during the summit discussions.