Pirate attacks more than doubled in Indonesia in the first nine months of 1999, prompting the International Maritime Bureau (IMB) to warn mariners to take urgent precautions in Indonesian waters. The number of actual and attempted pirate raids worldwide surged by more than 25 percent to 180 in the first three quarters of 1999, up from 143 in the same period in 1998, the IMB's Piracy Reporting Center in Malaysia's capital said in a report. Sixty-six of the attacks took place in Indonesian waters, up from 31 in January-September 1998, it said. There was also a dramatic increase in the number of raids in the Singapore Straits, adjacent to Indonesia, where 13 attacks were reported, compared to none in the first nine months of 1998. "Indonesian waters and the Indonesian part of the Singapore Straits remain piracy prone," it said in the 33-page report. "Pirates armed with knives and guns with fast speedboats are operating in these areas." It said pirates had boarded ships at anchor or under steam, assaulting crew and robbing them of cash and valuables. "Piracy in Indonesian waters is back to levels not seen since 1991," it said, noting that the rise could be attributed to Indonesia's economic and political troubles. "Mariners are warned to be extra cautious and to maintain anti-piracy watches when transiting Indonesian waters." The IMB said attacks had dropped off this quarter in the Singapore Straits, possibly indicating that authorities had stepped up patrols there. "However, there is no decline in incidents in Indonesian waters." Eight countries or regions accounted for more than two thirds of the 180 attacks in the first nine months of 1999 -- Indonesia (66), Singapore Straits (13), Malaysia (9), Nigeria (9), Somalia (8), Bangladesh (7), Brazil (6) and Venezuela (6). Attacks dropped from 10 to two in India and from 13 to four in the Philippines. Most of the attacks - 141 of 180 - involved pirates boarding ships. There was a decrease in the number of hijackings to six from 13. Half of the hijackings occurred in Somalia and Djibouti.