Somali pirates have stepped up their attacks in recent months.

Somali pirates have released a British-owned cargo ship, the Malaspina Castle, after more than a month following the payment of an undisclosed ransom.

The 32,000-tonne vessel, which has a mainly Bulgarian crew, was seized on 6 April in the Gulf of Aden while carrying a cargo of iron.

A Bulgarian government official confirmed the ship's release, saying the pirates' demands had been met.

He said that all members of the 24-strong crew were in good health.

Apart from 16 Bulgarians, they include several Russians, Ukrainians and Filipinos.

"The demands of the hijackers were met and the ship has been freed," said Bulgarian Deputy Foreign Minister Milen Keremedchiev.

Andrew Mwangura, coordinator of the East African Seafarers Assistance Programme, based in Mombasa, Kenya, confirmed the release of the vessel.

"It was freed today," he said on Saturday. "Ransom was paid a week ago."

Heavily armed Somali pirates continue to attack shipping in the Indian Ocean and Gulf of Aden despite the presence of international warships and a string of recent operations against them in recent months, some of which resulted in bloodshed.