Pirates have abducted 19 crew members of an oil tanker off the coast of Nigeria, a Greek company, the vessel operator, said.

The ship was attacked 77 nautical miles from Bonny Island on Tuesday. As a result 18 Indians and one Turk were abducted. Seven other sailors remain aboard a crude oil carrier for an Indian refinery, a spokesman for the Greek shipping company Navios Tankers Management said.

The Nigerian authorities reported that they are working on the case.

"We are doing everything necessary to make sure that the 19 crew members will return safe," the official at Navios said, adding that their families have been informed.

The ship can carry two million barrels of oil. The vessel was chartered by French oil company Total to deliver Bonny Light oil at Vizag in southern India, the source said. "Total has told us it would arrange alternative crew to get the cargo delivered on time," the source, who did not wish to be identified, told Reuters.

Nigerian Navy commander Captain Kolawole Oguntuga said the vessel, which loaded Shell Bonny Light, was hijacked soon after leaving the terminal. The ship did not request a navy escort to provide them with adequate protection, he said.