Russian forces have freed the crew of a Russian oil tanker seized by Somali pirates off the coast of Yemen, in a dramatic rescue operation.
Forces on the Russian warship Marshal Shaposhnikov approached the tanker with 23 Russian crew on board by helicopter.
As they did so, the pirates opened fire, sparking a shoot-out.
The Russian forces then abseiled onto the Moscow University tanker, freeing the crew who had locked themselves in a safe room after disabling their ship.
Ten pirates have been arrested, says the BBC's Richard Galpin in Moscow. They are currently being held aboard the tanker, Russian defence ministry spokesman Col Alexei Kuznetsov said.
They will be transferred to Moscow to face charges, reports say.
There have been unconfirmed reports that one pirate was killed during the siege.
"Pirates have released the tanker... All crew on board the tanker are alive and well," a spokeswoman for the Russian shipping company that owns the tanker, Novoship, told Reuters news agency.
"During more than 20 hours of siege, pirates were not able to take a single member of crew hostage."
Novoship praised the operation as one carried out "in the best traditions of the Russian naval mariners".
The decision to free the ship was made knowing "that the crew was under safe cover inaccessible to the pirates and that the lives and health of the sailors was not threatened by anything", Novoship added.
Although there are dozens of warships patrolling the Indian Ocean and the Gulf of Aden, it is rare for rescue efforts to be launched once pirates have boarded a vessel as it is often felt that intervening would endanger the hostages, says the BBC's Will Ross in Nairobi.
But in this case, the crew switched off the engine and locked themselves in a strong room with a reinforced door.
This tactic of retreating to a strong room has thwarted two previous hijacking attempts on other vessels, our correspondent adds.
The Moscow University was seized on Wednesday in the Gulf of Aden, off the coast of Yemen, as it sailed for China, carrying more than 80,000 tonnes of crude oil worth some $50m (£33m).
The Gulf of Aden is one of the world busiest shipping routes, and the Russians, Europeans and Americans have all deployed navy forces in the region after a growing number of attacks by pirates on commercial vessels, our correspondent adds.
Even so, pirates are reported to be holding more than 20 foreign ships with almost 400 sailors.
The Marshal Shaposhnikov was sent on Wednesday to rescue the hijacked tanker.