* Belgium arrests Somali pirate kingpin "Afweyne"
* Belgian undercover agents posed as film producers
* Prosecutors sought arrest over hijacking of Belgian ship "Pompei" (Updates with confirmation by federal prosecutors)
BRUSSELS, Oct 14 Belgium has arrested the suspected leader of a Somali pirate group after luring him to Brussels with promises to make a documentary about his money-making life on the high seas, prosecutors said on Monday.
Mohamed Abdi Hassan, known as "Afweyne" or Big Mouth, was detained when he arrived at Brussels airport on Saturday with another suspect identified as Mohamed M. A. or "Tiiceey", federal prosecutor Johan Delmulle told a news conference.
Tiiceey is a former governor of the Somali region of Himan and Heeb and is suspected in aiding Afweyne's pirate organisation, Delmulle said.
Prosecutors said they decided to involve Belgian undercover agents after it became clear that an international arrest warrant would not be successful in capturing the men.
"After patiently starting a relationship of trust with Tiiceey, and through him with Afweyne, which took several months, both were prepared to participate in this (film) project," Delmulle said.
The plan was put into action after two pirates were arrested and sentenced for the hijacking of a Belgian ship in 2009. Prosecutors decided to try to target the people behind the act, not only those who carried it out and so set up the sting.
"All too often those persons stay out of the frame and let others carry out their dirty business," Delmulle added.
The prosecutor said Afweyne was asked via Tiiceey whether he would be prepared to be an adviser on a film about piracy, portraying his life carrying out hijackings off the East African coast and making millions of dollars from ransom payments.
Prosecutors said it took months to reel Afweyne in and persuade him to come to Brussels, but would not provide further details about how the sting was carried out.
Afweyne said in January he had put his pirate days behind him and retired. United Nations experts have accused a former Somalian president of shielding him by issuing him a diplomatic passport.
In 2011, Somali piracy in the busy shipping lanes of the Gulf of Aden and the northwestern Indian Ocean netted $160 million, and cost the world economy some $7 billion, according to the American One Earth Future foundation.
But risks from pirate operations 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, taking foreign tourists and aid workers hostage in northern Kenya and Somalia. (Reporting by Robert-Jan Bartunek, Editing by Philip Blenkinsop and Ralph Boulton)