Nicaragua has sent a formal protest note to Colombia, saying a Colombian navy ship intimidated Nicaraguan fishermen in disputed waters.
Nicaragua's action is the latest twist in a long-running row between the two nations over several islets and a maritime border in the Caribbean Sea.
The UN's top court ruled in December that a treaty awarding three islands to Colombia was still valid.
The court said it could still rule on the border and island claims.
The Nicaraguan authorities handed a letter to Colombia's ambassador, accusing a Colombian frigate of confronting Nicaraguan fishermen on Sunday in what it said were Nicaraguan waters.
"This act and the location it happened can only be considered as a violation of Nicaraguan sovereignty," the letter said.
The Nicaraguan Foreign Minister, Samuel Santos, was planning to complain to UN Secretary General Ban Ki-moon about Colombia's alleged actions later on Wednesday.
The latest developments comes days after Nicaraguan President Daniel Ortega accused Colombia of stepping up military operations in the area, a claim swiftly rejected by Bogota.
Nicaragua's Daniel Ortega has stepped up the rhetoric recently
The issue of the maritime border between the two nations and claims over several islands were considered by the International Court of Justice last December.
In its ruling, the ICJ said that Colombian sovereignty over three islands in the area, San Andres, Providencia and Santa Catalina islands, had been legitimately settled in a 1928 treaty signed by both countries.
However, the court said it could rule on their maritime border and claims over other islets in the rich fishing waters.
The ICJ is seeking new submissions from Colombia and Nicaragua, although it could be months before the case comes before the court again.
The ICJ's rulings are binding.