Peter the Great, a Russian warship, is patrolling the area on anti-piracy duty.
The Russian navy says one of its warships has captured three pirate vessels off the coast of Somalia.
Ten pirates aboard the vessels were also detained, according to a statement given by the navy to news agencies.
A spokesman for the Russian navy said all those captured by the nuclear-powered warship, Peter the Great, were Somali nationals.
Pirates from Somalia target merchant ships sailing through the busy Gulf of Aden, which connects Europe and Asia.
Russian navy spokesman Igor Dygalo said the pirate boats were spotted by the warship's helicopter south-east of the Yemeni island of Socotra in the Indian Ocean.
"It was visually established how weapons were being dumped from the boats into the sea," Mr Dygalo said in a statement.
He said the navy seized weapons including grenade launchers and automatic rifles as well as a quantity of a "narcotic substance".
A multi-national task force including the United States, the UK, India and Russia currently patrol the sea off the unstable Horn of Africa to deter pirates.
On Thursday, the US navy said it had detained nine pirates.
The report of the Russian detentions came as the International Maritime Bureau issued a warning to shipping that the risk from piracy off the coast of Somalia was rising again.
The bureau's reporting centre in Kuala Lumpur says six ships were attacked this week alone, but all managed to escape.
The bureau blamed the heightened risk on more favourable weather and the temptation for pirates to target more ships for ransom, after recently releasing a number of hijacked vessels.
News of the Somali pirates' detention came on the same day the crew of a Ukrainian ship captured by Somali pirates arrived home at Kiev airport after a 19-week hijacking ordeal.
The MV Faina, released last week, docked on Thursday in Mombasa with its crew of 17 Ukrainians, two Russians and one Latvian, with a cargo of tanks and munitions.