While Africa remains problematic, Southeast Asia's Malacca Strait, one of the world's busiest waterways, has been relatively quiet, the International Maritime Bureau said in its report.

A total of 198 attacks on ships were reported between January and September this year, up from 174 in the same period in 2006, the IMB said.

It said a total of 15 vessels were hijacked, 63 crew kidnapped and three killed.

In the July to September period alone, there were 72 incidents, up from 47 in the same period a year earlier, marking the second straight quarterly rise in attacks, the London-based IMB said through its piracy reporting center in Kuala Lumpur, Malaysia.

"If this current trend continues, it would appear that the decline in piracy attacks since 2004 has bottomed out," it warned.

Indonesia remained the world's worst piracy hotspot, with 37 attacks in the first nine months of 2007 — but that was an improvement from 40 in the same period a year earlier, the IMB said.

Attacks rose rapidly in Somalia to 26 reported cases, up from only 8 a year earlier, it said. Somalia's U.N.-backed government has been struggling to assert control over the country since it accepted the aid of Ethiopian soldiers to chase a powerful Islamic alliance from power.

Nigeria also suffered 26 attacks so far this year, up from 9 previously.

IMB director Pottengal Mukundan urged ships to stay as far as possible from the coasts of Somalia and Nigeria, which remained dangerous with large numbers of violent kidnappings.

"The level of violence in high risk areas remain unacceptable. Pirates in Somalia are operating with impunity, seizing vessels hundreds of miles off the coast and holding the vessel and crew to ransom, making no attempt to hide their activity," he said.