The International Maritime Bureau says attacks by priates on merchant ships along the eastern and western coasts of Africa are intensifying and becoming more violent.
A report issued by the bureau says pirates have struck in international waters 102 times so far this year, down 28% compared with the same time last year.
But the ABC reports there's been an alarming rise in hijacks by Nigerian pirates and in Indonesian waters at the same time.
Bureau director Pottengal Mukundan said the Indonesian archipelago is increasingly seeing attacks by small-time sea-faring bandits, which he described as ''maritime muggings''.
The total cost of piracy was estimated to be between $US6.6 - $US6.9 billion.
