Massoel Shipping said in a statement Sunday that the ship MV Glarus, with 19 crew on board, was attacked as it was carrying wheat from the Nigerian commercial capital Lagos to Port Harcourt.
Reuters news agency reported late Sunday the Nigerian Maritime Administration and Safety Agency (NIMASA) had identified the nationalities of the kidnapped crew. It said seven crew members were from the Philippines and others were from Slovenia, Ukraine, Romania, Croatia and Bosnia.
Nigerian officials said the 12 were still unaccounted for.
Massoel Shipping said the vessel was attacked around 45 nautical miles southwest of Bonny Island early Saturday.
"It is understood the pirate gang boarded the Glarus by means of long ladders and cut the razor wire on deck to gain access to the vessel and eventually the bridge," the company said. "Having destroyed much of the vessel's communications equipment, the criminal gang departed, taking 12 of the 19 crew complement as hostage."
Piracy has been rising in the southern Niger Delta region in the past few years, along with the number sailors kidnapped for ransom.
According to a study published by the EOS Risk Group in July, the number of kidnappings in the region rose from 52 in 2016 to 75 last year. In the first half of this year, pirated kidnapped 35 sailors, it said.