The operators of a Greek oil tanker that disappeared off Angola insisted Monday that the vessel was seized by pirates, after Luanda dismissed the hijacking claim as "faked".
The 75,000-ton ship has since been found in Nigerian waters, but Luanda on Sunday denied that it had been hijacked by pirates.
The ship's operators Dynacom Tankers Management said however that the oil tanker MT Kerala had been hijacked close to the Luanda port, and that one of the crew members had been wounded in the incident.
A company source argued that the "unfounded" accusation by Angola that the hijacking was untrue was designed to offset responsibility for the incident.
"Angola is trying to cover up how a loaded vessel was taken in an area under its protection," the source told AFP.
"There will now have to be an investigation by US authorities and Interpol," the source added.
Dynacom earlier on Monday said it had re-established contact with the vessel on Sunday.
"All crew members are alive and accounted for, but one is wounded and all have clearly been affected by their ordeal," the company said, adding: "A large amount of cargo has been stolen."
The statement came after an Angolan navy spokesman said the tanker was at the entrance to the Luanda bay last Saturday when it was approached by a tugboat.
"It then cut off its communication system and followed the tugboat to Nigeria," said the spokesman.
"There is no piracy in Angolan waters," he said.
Dynacom said it had "engaged professionals experienced with these type of incidents" to resolve the incident.
The company said it had also worked with "European, North American and other international intelligence agencies" on the case.
Regional and international navies also "dispatched assets to monitor the pirates and provided support and assistance," it added.
The Kerala on January 18 had just loaded a shipment of diesel belonging to a subsidiary of Angola's state oil company Sonangol, when it went off the radar.
Sonangol has chartered MT Kerala since 2009 and its contract was due to end on February 12.
The Kerala carries a crew of 27 Indians and Filipinos.
It is currently en route to Ghana, the company source said.
Angolan experts such as maritime security agency Dryad Maritime, said the hijacking, if confirmed, would signal a spread of piracy from the Gulf of Guinea.
Despite emerging from a devastating civil war in 2002, Angola is one of the Africa's fastest developing economies, thanks to its oil resources.
It is the second largest oil producer in Africa after Nigeria, where crude oil theft is a problem, but has so far been spared the piracy woes dogging the west African oil giant.