BRUSSELS (REUTERS) - Belgium has arrested a suspected Somali pirate leader believed to have earned millions of dollars in ranson payments over years of operating off the East African coast.

Mohamed Abdi Hassan, known as "Afweyne" or Big Mouth, was detained when he arrived at Brussels Airport on Saturday, the De Standaard newspaper said on Monday.

Hassan is suspected of having commanded gangs that gained a fortune in ransom payments from merchant ships and yachts they seized over more than a decade of piracy. He said in January he had put his pirate days behind him and retired.

United Nations experts have accused a former Somalian president of shielding Hassan by issuing him a diplomatic passport.

In 2011, Somali piracy in the busy shipping lanes of the Gulf of Aden and the north-western Indian Ocean netted US$160 million (S$199 million), and cost the world economy some US$7 billion, according to the American One Earth Future foundation.

Risks from pirate operations, though, decreased following a step-up in patrolling by an international coalition of warships and greater use of private security guards on merchant ships.

Pirate groups have moved the focus of kidnappings to onshore.