NAIROBI, Kenya (AP)  -- Somali authorities have arrested six suspects in the hijacking of a U.N.-chartered cargo ship delivering food aid, officials said Tuesday.

The MV Rozen, however, remained under the control of four pirates who were aboard with 12 crew members as hostages, said the U.N's food agency.

The ship had been contracted to deliver aid to Somalia, where around 1 million people are suffering from a drought that hit the region last year, and had just delivered 1,800 metric tons (about 1,900 short tons) of food when it was seized.

Four suspected pirates were seized after they went ashore to buy supplies, Peter Goossens, the head of the U.N.'s World Food Program in Somalia, said in a statement. Sa'id Mohamed Raage, the regional fishing minister, said police arrested two others separately.

"The arrest is welcome news, but the safe release of the crew and the vessel remains our chief concern," Goossens said. "We very much hope this ordeal will finish soon."

The pirates are armed with AK-47 assault rifles and rocket-propelled grenade launchers, said Andrew Mwangura, head of the Kenyan chapter of the Seafarers Assistance Program, an independent group that monitors piracy in the region.

"Negotiations are under way to try and secure the release of the vessel," he added. The condition of the six Sri Lankan and six Kenyan crew members was unknown.

The ship, hijacked Sunday, has been anchored six miles (about 10 kilometers) off the coast of the semiautonomous Puntland region in northeastern Somalia, near Bargal.

Three Somali police speedboats have surrounded the boat, and a U.S. military vessel is patrolling the area and monitoring the situation.

"We are appealing for the safe return of the crew and the vessel as soon as possible, and for people to respect the need for humanitarian delivery corridors," Goossens said. "Somalia is one of the poorest countries in the world, and there are families whose lives depend on our ability to get food aid through."

The 1,860-mile (3,000-kilometer) coast of Somalia, which has had no effective government since warlords ousted a dictatorship in 1991 and then turned on each other, has become extremely dangerous for ships.

In southern Somalia, Mohamed Abdi, a fishermen, complained that people he says are U.S. marine or naval officers stopped fisherman from eight boats, taking them to their ship about 500 miles (805 kilometers) away from the Somali coast to question them for about two hours late Monday.

Abdi, speaking on the phone from Marka, a port town about 56 miles (90 kilometers) southwest of the Somali capital, Mogadishu, said that the officers wanted to find out whether the fishermen were pirates or have links with Somalia's Islamic movement that was ousted in December from its southern Somalia strongholds.

"We urge government officials to plead our case to the U.S. government because the interruption affects our earnings. We use boats for fishing, but not for other illegal purposes. We are not sea pirates, and we are not sympathizers of terrorists," Abdi said.

Somalia's national Minister Fisheries Hassan Abshir Farah said that the U.S. officials' actions were acceptable because Somalia does not have its own coast guard and its coastline "has been considered one of the worst waters in the world."

Somali pirates are trained fighters, often dressed in military fatigues, using speedboats equipped with satellite phones and global positioning system equipment. They are typically armed with automatic weapons, anti-tank rocket launchers and various types of grenades, according to the U.N. Monitoring Group on Somalia.

The bandits target both passenger, cargo and fishing vessels for ransom or loot.

Source: AP