The pirates were seized inside the Indian Ocean archipelago's territorial waters after they used automatic weapons to attack a Seychelles coastguard vessel in December.

"These convictions will ... serve as a deterrent for prospective Somali pirates who would otherwise have thought they would have come into Seychelles waters with impunity," a statement from Seychelles Department of Legal Affairs said.

All 11 pirates were sentenced to 10 years in jail, with eight of them found guilty of committing acts of piracy and three for aiding and abetting pirates.

Somalia has lacked an effective central government for nearly 20 years and does not have the legal infrastructure to support trials. Captured pirates are often released because of disagreements over who should try them and a lack of evidence if weapons have been thrown overboard.

In May, Kenya threatened to terminate its agreement to prosecute pirates if other nations did not share the financial burden.

Another 29 suspected Somali pirates remain in detention on the palm-fringed islands that are better known as an exclusive retreat for celebrities and tycoons.