Costa Rica's top diplomat voiced alarm Sunday that Nicaragua is boosting its military ties to Russia, in his view to the point of dependency.
"Russia is facilitating the arming of Nicaragua — ships — and they have spoken about buying jets and other weapons. I fear problems are in store," Foreign Minister Enrique Castillo told La Nacion daily.
The two Central American nations have border disputes before the International Court of Justice.
Castillo said he believed there was cause for concern that Managua's leftist government "is being armed, and is entering into a relationship of military dependency with Russia."
Last month, Nicaraguan President Daniel Ortega said his country was "committed to further strengthening and modernizing the army" with the help of any country willing to provide aid.
He did not give details of an agreement between Nicaragua and Russia.
But Russia's ambassador in Managua had confirmed in March that Moscow is interested in building a military resupply base in Nicaragua.
Russian defense chief Sergei Shoigu has said that Russia is weighing increasing its military presence in countries including Nicaragua, Cuba and Venezuela — particularly bases to refuel Russian warplanes far from home.
All three of the countries Shoigu mentioned are leftist allies and harsh critics of the United States.
Nicaragua Army Chief General Julio Aviles had said this was just "speculation."
And Nicaraguan authorities have said that there was no talk of Russian bases in Nicaragua, but rather of potential refueling and resupply of Russian jets and/or ships.
Russian Foreign Minister Sergei Lavrov visited Nicaragua last week, and met with Ortega on a trip that also took him to Chile, Cuba and Peru.
Russia has faced international condemnation over its actions in Crimea, which has switched to Moscow from Ukraine after pro-Russian forces seized the peninsula.
Crimea is a top strategic interest for Russia since it hosts Moscow's only warm-water port open year-round.