Updated

Sea piracy fell 54 percent worldwide in the first half of 2012, led by a dramatic drop in Somali piracy, an international maritime watchdog said Monday.

The International Maritime Bureau attributed the sharp drop to anti-piracy operations by international navies patrolling in seas off Somalia as well as increased vigilance by ships, including the hiring of private armed guards on board.

The bureau said 177 attacks were reported worldwide from January to June, down from 266 in the same period last year. It said 20 vessels were hijacked, with 334 crew members taken hostage and at least four crew members killed.

Attacks off Somalia's coast plunged to 69 in the first six months from 163 a year earlier, it said. Somali pirates were able to seize 13 vessels, down from 21.

"The naval actions play an essential role in frustrating the pirates. There is no alternative to their continued presence," said IMB Director Pottengal Mukundan. He warned that Somali pirates remain a serious threat, with 11 vessels and 218 crew members still in their hands as of late June.

A separate report by the U.N. Monitoring Group on Somalia and Eritrea warned that pirate militias are adapting to their harsher operating environment by turning to new types of criminal activity, such as ransom kidnappings on land of aid workers, journalists and tourists.

The maritime bureau said the decline in Somali piracy was partially offset by intensified attacks in the Gulf of Guinea off western Africa, where 32 cases including five hijackings were reported, up from 25 in the first half last year.

The bureau said attacks by armed pirates in skiffs were occurring further from the gulf's coast, suggesting the possible use of fishing or other vessels to reach targets. London-based Lloyd's Market Association, an umbrella group of insurers, last year listed Nigeria, Benin and nearby waters in the same risk category as Somalia.

Elsewhere, the bureau said attacks have mainly been armed robberies, with Indonesia reporting 32 cases, up from 21 a year ago.

Also Monday, the EU announced a new plan to boost the naval capabilities of nations in the Indian Ocean which have been helping battle piracy off Somalia.

The program will initially cover Djibouti, Kenya, and the Seychelles. Tanzania will be added soon, an EU statement said.

Since, 2008, the EU has maintained a flotilla consisting of between five and 10 warships off the Horn of Africa, as part of a larger international fleet that includes U.S., NATO, Russian and other warships. The EU task force also includes non-EU countries such as Norway, Croatia, Montenegro and Ukraine.

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Associated Press writers Slobodan Lekic in Brussels and Jason Straziuso in Nairobi, Kenya, contributed to this report.