Costa Rica on Monday asked the Organization of American States to call an urgent meeting to address an alleged incursion by Nicaraguan troops onto Costa Rican soil.
Security Minister Jose Tijerino said more police had been sent to the northeastern border with Nicaragua after authorities detected Nicaraguan troops on Calero, an island in the San Juan River claimed by Costa Rica.
"The police will be properly equipped ... but we will avoid, as much as we can, a confrontation that will only aggravate the situation," Tijerina said.
The border river has been a source of disputes between the Central American neighbors for nearly two centuries. Last year, the United Nations' highest court set travel rules for the San Juan, affirming freedom for Costa Rican boats to navigate the waterway while upholding Nicaragua's right to regulate traffic.
In their latest dispute, the two nations have been squabbling over Nicaragua's dredging in the river. Costa Rica claimed the work was causing environmental damage on its soil, a charge Nicaragua denied.
Costa Rica said that after receiving reports of Nicaraguan soliders on its soil, it initially sent some 70 police reinforcements to the border area Oct. 22. That was the day after Costa Rica formally complained to Nicaragua's ambassador about the dredging.
The Nicaraguan government denied Monday that it has caused environmental damage, and said its troops have not intruded on Costa Rican territory.
Nicaragua's army chief of staff, Gen. Julio Aviles, said the soldiers are on the Nicaraguan side of the border as part of an anti-drug operation.
Aviles contended the allegation about Nicaraguan troops violating Costa Rican territory was made by members of a Nicaraguan family living in San Jose, Costa Rica's capital. He alleged the family is involved in drug trafficking and is trying to undermine the Nicaraguan army's anti-drug fight.
"The army has always maintained a constant guard on the San Juan River in its fight against international drug trafficking and at no time has violated international norms and treaties, nor has it invaded foreign territory," Aviles said.