Mystery shrouds the alleged attack on an offshore tug at a Ghanaian port on Thursday with officials at the port unaware of the incident.

The International Maritime Bureau's Piracy Reporting Centre received word of a boarding of an offshore tug at the port of Takoradi at 04:00 local time.

The report said four robbers armed with long knives stole ship stores and threatened the duty watchman before fleeing in a canoe. There were no injuries to crew, however.

One informed source said the tug, described as a supply vessel, was Liberia-flagged and about 2000 gross tonnes.

However, the harbor master at Takoradi port was unaware of any such incident when contacted by Upstream on Thursday, despite having received two reports of activity at the port overnight, neither of which yielded anything untoward.

The report to the IMB is understood to have been made directly by the vessel's owning/managing company, which, along with the vessel name, has not been revealed.

Security incidents involving offshore vessels and structures off Nigeria often go unreported.