Ecuador says it has arrested five alleged members of the Colombian rebel group Farc inside its territory.
Ecuador has moved soldiers towards its border with Colombia
Defence Minister Gustavo Larrea said the suspected rebels were detained by the army during a search of farms and houses close to the Colombian border.
It comes amid a growing crisis over a Colombian raid inside Ecuador in which a senior Farc leader was killed.
On Thursday Nicaragua said that like Venezuela and Ecuador it was breaking diplomatic relations with Colombia.
Nicaraguan President Daniel Ortega said "we are breaking off relations because of the political terrorism" carried out by Colombian President Alvaro Uribe.
He made the announcement in the Nicaraguan capital, Managua, with Ecuadorean President Rafael Correa at his side.
Mr Correa is on a tour of Latin American capitals to rally opposition to Colombia's cross-border raid on Saturday.
Venezuela and Ecuador have already broken off diplomatic ties and moved troops to their borders with Colombia following the raid in which Raul Reyes, a prominent member of the leftist Revolutionary Armed Forces of Colombia (Farc), and at least 23 other rebels were killed.
Announcing Ecuador's arrest of five alleged rebels, Mr Larrea said that they had been detained very close to the Colombian border.
"The guerrillas were detained in the Chanangue river, which leads to the San Miguel River, located very few metres from the Colombian border."
He said that they had been discovered by an army patrol searching homes for any signs of residents sheltering guerrillas.
Tensions throughout the region have risen since Colombia's raid in which Reyes died.
Venezuela says 9,000 soldiers have been moved to the border with Colombia, while Ecuador says 3,200 of its forces have been deployed.
President Ortega is an ally of Ecuador's President Correa
Latin American leaders have urged calm and US Secretary of State Condoleezza Rice has called for a "diplomatic resolution" to the crisis.
Colombia has apologised to Ecuador but said the raid was necessary.
"The situation shows that everyone needs to be vigilant about the use of border areas by terrorist organisations like the Farc," Ms Rice told a news conference in Brussels after a meeting of Nato foreign ministers.
The presidents of Ecuador and Venezuela have called for clear international condemnation of Colombia's actions.
An opportunity for talks could arise in the Dominican Republic, where regional leaders are gathering for a meeting of the Rio Group.
Latin American presidents, including those from Colombia, Venezuela and Ecuador, are expected to meet on Friday.
The Organization of American States (OAS) on Wednesday unanimously approved a resolution saying that Colombia had violated the "principles of international law" by crossing into Ecuador, but stopped short of an outright condemnation.
The 34 OAS member states agreed to set up a commission of inquiry led by OAS head Jose Miguel Insulza to investigate the incursion and scheduled a meeting of OAS foreign ministers for 17 March.
Colombia has waged a four-decade conflict with left-wing rebels who finance themselves through the cocaine trade and by kidnapping hostages for ransom or political gain.
Venezuelan President Hugo Chavez had become involved in mediation efforts to free Farc-held hostages in Colombia, securing the release of six this year.
He branded the Colombian raid a "war crime", adding that Bogota, which receives billions of dollars in aid from Washington to fight drug-trafficking, was just a "lackey of United States imperialism".
He dismissed Colombian claims that a laptop found during its raid on the rebel camp in Ecuador held files indicating that Venezuela had given the Farc $300m (£150m).