By Will Grant
Americas editor, BBC News
Hugo Chavez's declaration that he will have nothing more to do with Alvaro Uribe as long as he is in power takes relations between Venezuela and Colombia to probably their worst point in the past 20 years.
A short-lived warming in ties soon deteriorated into a fresh chill
Not since a Colombian military vessel entered disputed waters in 1987 has the relationship deteriorated this badly.
The relationship between Mr Chavez and Mr Uribe has always been strained - the former is an outspoken socialist president who relishes in criticising the US and its policies, while the latter is Washington's closest ally in Latin America.
This specific problem came about after Mr Uribe granted Mr Chavez permission to get involved with the complex process of negotiating with the left-wing rebel group, the Farc.
After a series of diplomatic incidents and lapses of protocol, the Colombian leader withdrew that authority from President Chavez.
Chavez responded by recalling his ambassador from Bogota and calling Mr Uribe a liar and a pawn of the US.
But some analysts believe there is a strong domestic element to this move by President Chavez.
On Sunday, Venezuelans will vote on a series of proposed constitutional changes, among them a measure to remove the limit on the number of terms the president can stand for office.
Some polls predict that the referendum will be close-fought, and the opposition has said that the current diplomatic crisis with Colombia has more to do with diverting attention away from the vote.