Somali pirates have released a Yemeni cargo ship they seized last week after successful negotiations between regional authorities, clan elders and the gunmen.

A surge in attacks at sea this year in the busy Gulf of Aden and Indian Ocean off Somalia has pushed up insurance costs, brought the gangs tens of millions of US dollars in ransoms, and prompted foreign warships to rush to the area.

The MV Amani, owned by Yemeni shipping firm Abu Talal, had seven sailors on board.

It was seized on 25 November as it carried 507 tonnes of steel from Yemen's Mukalla port to Socotra Island.

Eyl is a remote former fishing village on the Puntland coast that has become well-defended base for the pirates.

There have been nearly 100 attacks in Somali waters this year, despite the presence of several foreign warships.

The sea gangs are believed to be holding about a dozen ships and nearly 300 crew.

Among the captured vessels are the Sirius Star, a Saudi supertanker loaded with €79m of crude oil and the MV Faina, a Ukrainian cargo ship carrying some 30 Soviet-era tanks.

On Tuesday, the UN Security Council renewed its authorisation for countries to use military force against the gunmen operating off the anarchic Horn of Africa nation.