The head of a Polish shipping company says the captain and four other Polish seamen abducted from a ship off Nigeria's coast last week are alive.

Michal Czerepaniak, head of Polaris Maritime Services in Szczecin, said on Polish radio Sunday that the five were "safe and sound." He gave no further details.

Poland's Foreign Ministry could not immediately confirm the information but was planning a statement later Sunday.

Armed attackers abducted the captain, three officers and a seaman from the MV Szafir cargo ship in Nigerian waters on Thursday. The remaining 11 crew members barricaded themselves inside the ship and were left unharmed.

The ship was being brought to a naval port in Nigeria while Nigerian and Polish authorities continued efforts to have the abducted crewmen released.