The vessel, the MV Nimatullah, was delivering nearly 900 tons of cargo when about 10 pirates in a speedboat overpowered the 14-member crew early Monday, said Andrew Mwangura, head of the Kenyan chapter of the Seafarers Assistance Program.
"The crew told us by telephone that they had been hijacked by Somali pirates," said Hussein Ali Jillow, a Somali businessman who hired the cargo ship. "The crew did not say anything about their conditions."
No ransom has been demanded, Mwangura added.
In February, Somali pirates seized a U.N. chartered vessel that had just delivered food aid in northeastern Somalia. The 12 crew still remain hostage.
The 1,860 mile-coast of Somalia, which has had no effective government since warlords ousted a dictatorship in 1991 and then turned on each other, has emerged as one of the most dangerous areas for ships.
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.
In 2005, two ships carrying U.N. World Food Program aid were overwhelmed by pirates. The number of overall reported at-sea hijackings that year was 35, compared with two in 2004, according to the International Maritime Bureau.