Venezuela has ordered troops to its border with Colombia in response to the killing by Colombian troops of a left-wing rebel leader on Ecuador's territory.
By Warren Bull
BBC Americas analyst
Mr Uribe (seated) was at the funeral of a soldier killed in the operation
Possibly the only thing that unites the presidents of Colombia and Venezuela is their resolve to view the world differently.
Alvaro Uribe is a former lawyer educated at Harvard and Oxford, and a political conservative who believes in free trade.
Since coming to power in Colombia in 2002 he has maintained a hardline policy against the Farc rebel movement, which killed his father during a kidnap attempt.
Mr Uribe's policies have brought him close ties with Washington, and billions of dollars in American aid for the fight against the rebel insurgency and drug trafficking.
In contrast, Venezuelan President Hugo Chavez is a former paratrooper and the charismatic leader of the new left in Latin America.
Backed by vast oil reserves, he has attempted to direct the continent away from the influence of Washington.
For Mr Chavez, that role includes offering to use his influence in hostage negotiations with the Farc, who regard him as an ally.
Impact on hostages
Last year, Mr Uribe felt under pressure to achieve the release of hostages held by the Farc.
Mr Chavez has been mediating hostage releases with the rebels
He accepted the mediation of Mr Chavez but quickly cancelled the role, saying the Venezuelan president had broken protocols.
He also accused the Venezuelan leader of using the mediation to give the guerrillas a more prominent political role, and expand his personal influence in the region.
Mr Chavez responded by ending diplomatic contacts with Colombia, and in December threatened to cut trade ties.
But against Bogota's wishes Mr Chavez also decided to continue his dialogue with the Farc - a position which gained approval from the families of many hostages, and leading figures in the international community who wanted to see positive results.
This included the French government, which was particularly concerned about the fate of the Colombian-French politician Ingrid Betancourt.
Since January, the rebels have delivered six hostages into his care in Venezuela, as they seek a wider exchange of captives for jailed guerrillas.
But the latest assault indicates that the Colombian president still believes the best way to get the rebels to negotiate is by weakening them militarily.
For Mr Chavez, it was unacceptable that Colombian forces would kill Raul Reyes - a man he regarded as a "good revolutionary" - in the territory of his political ally, Rafael Correa.
But despite the threat of war by Mr Chavez, it is hard to see the situation escalating into a full-blown conflict with Colombia.
The two presidents may remain political foes until they end their terms in office, but they are unlikely to become military ones, if only because most Colombians and Venezuelans do not have the stomach for it.
What is likely in the short term is that there will be no more hostage releases.