Sea piracy worldwide dropped slightly in 2011 for the first time in five years but Somali pirates have intensified attacks and remained the greatest threat, a global maritime watchdog said Thursday.

The number of attacks dipped to 439 last year from 445 cases in 2010, the International Maritime Bureau's piracy reporting center in Kuala Lumpur said in a report.

There were 45 vessels hijacked and 802 crew members taken hostage, as compared with 53 ships seized and 1,181 people taken hostage in 2010.

The agency attributed the decline to international naval patrols and increases in private security personnel aboard ships.

Somali pirates accounted for 54 percent of the global attacks with 237 cases, up from 219 in 2010, it said.

The IMB said Somali pirates for the first time hijacked a vessel at anchorage in Oman, indicating they were desperate. This highlighted the need for ports and vessels at anchorages in the region to be vigilant, it said.

"The role of the navies is critical to the anti-piracy efforts in this area," said IMB Director Pottengal Mukundan.

Lawless Somalia's long coastline snakes around the Horn of Africa and provides the perfect base for pirate dens. The country has not had a functioning government since a socialist dictatorship collapsed in 1991, plunging the nation into clan-based civil war.

An international flotilla of warships patrols waters threatened by Somali pirates, particularly the Gulf of Aden corridor leading to the Suez Canal. Attacks in that area fell 43 percent to 37 attacks in 2011.

Elsewhere, the IMB said Benin emerged as a piracy hotspot with 20 attacks on tankers last year, of which eight were hijacked. Another 10 attacks occurred in neighboring Nigeria but the IMB said it was aware that at least another 34 incidents in the country went unreported.

Although ships seized in Nigeria and Benin were usually released within 10 days, compared to six months in Somali hijackings, the IMB warned that these attacks could become more violent.

Sea robbery rose in Indonesia for a second straight year to 46 attacks, up from 40 in 2010.

But pirate attacks in the South China Sea plunged to 13, from 31 in 2010. Bangladesh also showed improvement with only 10 attacks, from 23 in 2010, thanks to initiatives taken by its coast guards, the IMB said.