(CNN) -- Pirates traded gunfire with Togo security forces early Tuesday from a hijacked oil tanker off the west coast of Africa, the International Maritime Bureau said.
"Apparently there was an exchange of fire between pirates on board the hijacked tanker and the naval patrol vessel," said Cyrus Mody, spokesman for the maritime bureau, based in London.
A representative for Golden Energy Management, the Greek company that chartered the vessel, said there were 24 crew members on board, all of them Russian. The representative had no information on the condition of the crew and said company officials in Athens have been unable to establish contact with the sailors.
The Isle of Man-flagged Energy Centurion was seized off the coast of the Togolese capital Lome, where it was anchored.
A security official in Togo said authorities received the alert from the oil tanker around 2 a.m.
"We quickly sent patrols after it, but we did not succeed in catching the pirates who took control of the tanker and disappeared off the coast of neighboring Benin," said Col. Djibril Inoussa, the communications director of Togo Armed Forces.
This is the second such attack in less than two weeks in the Gulf of Guinea, off the west coast of Africa.
"This has been an area of risk and a hotspot for a number of years," said Mody. He said the number of piracy incidents in Nigerian waters has been severely under-reported, and tend to be overshadowed by Somali piracy.
While Somali piracy remains a serious threat, there has been an increase of attacks in the Gulf of Guinea, according to a recent report from International Maritime Bureau's Piracy Reporting Center.
The report said there were 32 attacks this year in the Gulf of Guinea -- including five hijackings, versus 25 in 2011.
The main difference between the East and West African pirate activities is that almost all the incidents in Nigeria are conducted within its territorial waters, whereas most of the incidents along the eastern coast of Africa and the Gulf of Aden occur on the high seas, according to the maritime bureau.
Mody said it is possible that the same group responsible for Tuesday's attack was involved in the hijacking of a UK-operated oil tanker August 19. That vessel was later released off the coast of Nigeria.
"Their modus-operandi is to target mainly oil tankers, and steal the cargo," said Mody. He said refined oil -- gas or diesel -- is easy to sell on open black markets. The hijacked vessel is then either taken to the same location where it was picked up, or moved to another site and released.
Mody said pirates also go through each crew cabin to see what they can take. He said crews are often beaten up, sometimes severely.
"Nigerian incidents tend to be very violent towards the crew," Mody said.
Journalists Erick Kaglan in Togo and Elinda Labropoulou in Athens contributed to this report