Updated

Gunmen attacked a supply tug boat off the coast of Nigeria's oil-rich southern delta, kidnapping four foreign sailors in the latest attack in the West African region that is increasingly dangerous for shippers and oil companies, officials said Monday.

The attack happened 40 nautical miles off the coast of Bayelsa state in the Niger Delta on Sunday night, as the gunmen stormed the moving vessel, the International Maritime Bureau said Monday in a warning to other shippers. The gunmen seized four workers and later fled, the bureau said. Those remaining onboard safely guided the ship to a nearby harbor, the bureau said.

The bureau did not identify the shipper, nor the sailors. However, a separate notice to private security contractors working in Nigeria and seen by The Associated Press identified the four hostages as foreigners.

In Rome, the Foreign Ministry confirmed the kidnapping, saying the four hostages were members of the crew. A Foreign Ministry official said three of the four were Italian. The official, who spoke on condition of anonymity because he was not authorized to release the information publicly, said he didn't know the nationality of the fourth hostage.

Foreign Minister Giulio Terzi was following the case personally, and the ministry was working with Nigerian officials to secure the safe return of the crew, the official said. The official and the private security notice seen by the AP identified the vessel attacked as the Asso Ventuno, operated by Augusta Offshore SpA, a Naples-based shipping company.

Calls to the company were not successful on Monday, Christmas Eve. Someone who answered the phone hung up when contacted by the AP, and then didn't pick up on subsequent calls. The company's website says it does business with oil companies Total SA and Exxon Mobil Corp. in Nigeria.

Commodore Kabir Aliyu, a spokesman for Nigeria's navy, declined to immediately comment Monday.

Pirate attacks are on the rise in West Africa's Gulf of Guinea, which follows the continent's southward curve from Liberia to Gabon. Over the last year and a half, piracy there has escalated from low-level armed robberies to hijackings and cargo thefts. Last year, London-based Lloyd's Market Association — an umbrella group of insurers — listed Nigeria, neighboring Benin and nearby waters in the same risk category as Somalia, where two decades of war and anarchy have allowed piracy to flourish.

Analysts believe many of the attackers come from Nigeria, whose lawless waters and often violent oil region routinely see foreigners kidnapped for ransom. Increasingly, criminal gangs also have targeted middle- and upper-class Nigerians as well.

Typically, foreign companies operating in Nigeria's Niger Delta pay cash ransoms to free their employees after negotiating down kidnappers' demands. Foreign hostages can fetch hundreds of thousands of dollars apiece.

Foreign companies have pumped oil out of the Niger Delta, a region of mangroves and swamps the size of Portugal, for more than 50 years. Despite the billions of dollars flowing into Nigeria's government, many in the delta remain desperately poor, living in polluted waters without access to proper medical care, education or work. The poor conditions sparked an uprising in 2006 by militants and opportunistic criminals who blew up oil pipelines and kidnapped foreign workers.

That violence ebbed in 2009 with a government-sponsored amnesty program that offered ex-fighters monthly payments and job training. However, few in the delta have seen the promised benefits and sporadic kidnappings and attacks continue. The end of the year in Nigeria usually sees an uptick in criminal activity as well, as criminal gangs target the wealthy returning to the country to celebrate the holidays.

Sunday's kidnapping is just the latest attack in the region. On Dec. 17, gunmen kidnapped five Indian sailors on the SP Brussels tanker as it sat about 40 miles (64 kilometers) off the coast of the Niger Delta. That came the same day gunmen abducted four South Koreans and a Nigerian working for Hyundai Heavy Industries Co. at a construction site in the Brass area of Bayelsa state. Those workers were later released, though the Indians are still believed to be held by the abductors.