Two or three pirate speedboats were chasing the Dutch ship, with the goal of boarding it, when the Russians intervened, said Capt. Pottengal Mukundan, director of the International Maritime Bureau in London.
He said the pirates fired two rocket-propelled grenades at the Dutch ship, but no injuries were reported.
The incident occurred about midday Tuesday.
The Russians chased one of the speedboats but the pirates got away, Mukundan said. He said he didn't know where the Dutch ship was headed