By Warren Bull
BBC Americas analyst
The crisis between Colombia and its two neighbours, Ecuador and Venezuela, has drawn strong reactions from leaders across the Americas.
The Farc has been causing misery for decades, Washington says
Washington has poured billions of dollars of aid into Colombia to fight the rebel insurgency.
It was no surprise, then, that the US state department spokesman, Tom Casey, said the United States supported Colombia in its efforts to respond to what he called the "threat and challenge" of the Farc, which he described as a terrorist organisation.
Mr Casey said the Farc rebels "have been making life miserable for the people of that country for more than 20 years, and certainly there should be no one out there under any illusions as to what kind of organisation they are".
Mr Casey also questioned the involvement in the affair of Venezuela, which like Ecuador, has ordered troops to the border with Colombia. The US has sought to curtail the influence of Venezuelan President Hugo Chavez in the region, and would like to cast the problem as a bilateral affair between Bogota and Quito.
But Washington is unlikely to be a major player in any solution to the crisis - that role will almost certainty be taken by leaders from Latin America. They will have their chance on Tuesday, at an emergency meeting of the Organisation of American States (OAS).
Brazil as mediator?
Border sovereignty in Latin America is a sensitive issue, and its leaders will be under no illusions about the seriousness of the situation.
The last time there was a regional dispute involving a border, between Ecuador and Peru in 1995, more than 100 people are believed to have been killed in the resulting hostilities.
Peru is among the countries which have lined up to criticise Colombia's actions, while more still have urged restraint.
But the prospective leader of the diplomatic offensive is Brazil, the largest country in South America, a supporter of regional co-operation, and one which has mainly cordial relations with the three presidents involved.
A sign of Brazil's likely strategy comes from its Foreign Minister, Celso Amorim, who says the OAS should set up a commission to investigate the facts.
"The territorial violation is very serious and needs to be condemned," said Mr Amorim on Monday, adding that it was up to Colombia to make a positive move. "A more explicit apology to Ecuador for the territorial violation would help contain the crisis."
That may be the only generally accepted way to get all sides to step back from the edge.