The waters off Somalia are among the most dangerous in the world
A Ukrainian ship seized by pirates off the coast of Somalia was carrying 33 tanks and other weapons, the Ukrainian defence minister has confirmed.
Earlier, the country's foreign ministry said the ship had a crew of 21 and was sailing under a Belize flag to the Kenyan port of Mombasa.
There has been a recent surge in piracy off the coast of Somalia.
Russia announced on Friday it would start carrying out regular anti-piracy patrols in the waters off Somalia.
A navy spokesman said a warship had been sent to the area earlier this week to protect Russian citizens and ships.
Somalia has not had an effective national government for 17 years, leading to a collapse of law and order both on land and at sea.
Somali pirates are currently holding more than a dozen hijacked ships in Eyl, a town in the semi-autonomous region of Puntland.
Senior UN officials estimate the ransoms pirates earn from hijacking ships exceed $100m (£54m) a year.
It was not immediately clear where the Ukrainian ship had been taken.
The Ukrainian foreign ministry said the captain of the Faina cargo ship had reported being surrounded by three boats of armed men on Thursday afternoon.
Defence Minister Yury Yekhanurov confirmed that 33 Russian T-72 tanks and "a substantial quantity of ammunition" were aboard.
He said all the weapons had been sold in compliance with international agreements.
Earlier reports suggested that the cargo was destined for south Sudan, however Kenyan government spokesman Alfred Mutua confirmed that the tanks were going to Kenya.
"The cargo in the ship includes military hardware such as tanks and an assortment of spare parts for use by different branches of the Kenyan military," he said.
Security analyst Knox Chitiyo told the BBC that the incident showed that the waters off Somalia's coast had become a "global security problem".
"Piracy has become big business and there seems to be no concerted response to the problem," said Mr Chitiyo, from the London-based Royal United Services Institute.
Last week, France circulated a draft UN resolution urging states to deploy naval vessels and aircraft to combat piracy in the area.
France has intervened twice to free French sailors kidnapped by pirates. Commandos freed two people whose boat was hijacked in the Gulf of Aden earlier this month.
After an earlier raid in April, six arrested pirates were handed over to the French authorities for trial.
International navies have been escorting humanitarian deliveries to Somalia, where a third of the population needs food aid.
Pirates have seized dozens of ships from the major shipping routes near Somalia's coast in recent months.
Pirate "mother ships" travel far out to sea and launch smaller boats to attack passing vessels, sometimes using rocket-propelled grenades (RPGs).
Authorities in Somalia's semi-autonomous region of Puntland say they are powerless to confront the pirates, who have been growing in strength.
International navies have been escorting aid deliveries
In Eyl, where ships are held for ransom, a flourishing local industry has developed.
Insurgents in Somalia, not known to have links to the pirates, are currently battling a combination of government troops, their Ethiopian allies and African Union peacekeepers in Mogadishu and other parts of southern Somalia.
The US has an anti-terror task force based in neighbouring Djibouti and has carried out several air strikes against the Islamic insurgents, accusing them of sheltering al-Qaeda operatives.