Updated

Greek authorities say an oil tanker has come under armed attack off the west coast of Africa, and the ship's Ukrainian captain and Greek first engineer have been kidnapped.

The Merchant Ministry said Tuesday about 10 armed men boarded the Marshall Islands-flagged Althea about 35 nautical miles south of Nigeria.

The ship's management company, Medtankers, said 18 officers and crew were on board, all Ukrainian apart from the first engineer. The men were robbed of personal items but none were hurt in the overnight attack, and the ship's cargo of oil was untouched.

Ship hijackings and kidnapping for ransom have increased in the oil-rich Gulf of Guinea in the past year, making it the world's piracy hotspot, overtaking the Indian Ocean waters off Somalia.