There are three Russian, 17 Ukrainian and one Latvian national on board the Ukrainian-owned Faina ship flying the Belize flag, the ministry said late Thursday, referring to the ship owner, Tomax Team Inc.
Tomax said the vessel's captain contacted the company to say three boats with armed men on board had approached the ship, after which contact was lost.
Earlier reports said the Ukrainian vessel was carrying military equipment, possibly about 30 T-72 tanks.
The Foreign Ministry said information on the cargo was being verified, adding that Ukraine's embassies in Britain and Kenya had been instructed to check reports on the seizure.
Pirates are increasingly active in the waters off Somalia, which has no effective government and no navy to police its coastline. The International Maritime Bureau said more than 30 incidents of piracy were registered in the region in 2007. More than 30 attacks have been committed so far this year off the coast of the East African nation.
