Pirates boarded an oil industry supply vessel off Nigeria on Wednesday and seized three French seamen, in the second hostage drama for French energy workers in West Africa in less than a week. The men's employer, French maritime services firm Bourbon, and the French foreign ministry said they had contacted the kidnapped workers' families and were working with Nigerian authorities to secure their release. "Everything points to it being a classic act of piracy," French Defence Minister Herve Morin told France 24 television, playing down speculation that the hostage-takers may have had a political motive. A spokesman for the Nigerian military taskforce deployed to protect the west African giant's oil industry confirmed the attack, but said that in total four hostages were taken. There have been no reports of ransom demands. Wednesday's drama came just six days after five French nationals working in neighbouring Niger's uranium fields were kidnapped by Al-Qaeda militants, in an unrelated attack that has already stretched French assets in the region. The sailors were abducted when pirates equipped with several speedboats attacked the French-flagged Bourbon Alexandre, a 2,000-tonne tug and supply ship working in waters off Nigeria's restive Niger Delta region. "The 13 other crew members have remained on board and nobody has been injured. No claim has been made at this stage," Bourbon said in a statement. Bourbon did not say exactly where the attack took place, but said its boat had been working on a field owned by Addax Petroleum, a Swiss-based subsidiary of the Chinese energy and chemical giant Sinopec. Addax has several offshore and onshore fields in Nigeria, but its main offshore wells lie in OML123, an oil production bloc 60 kilometres (37 miles) south of the city of Calabar at the far eastern edge of the Niger Delta. After the seaways off Somalia, the Gulf of Guinea south of Nigeria is one of the world's most notorious pirate hunting grounds, and ships working in the region's huge oil industry are often targeted by kidnap and ransom gangs. Some of the gangs are purely criminal, while others claim to be fighting for the independence of the delta region, a swathe of mangrove forests and salt water swamp that is home to one of Africa's largest oil industries. In most cases, hostages are released in exchange for undisclosed ransoms, and it is extremely rare for foreign workers to be hurt or killed -- although many find themselves held for weeks or months in remote villages. "I think, from memory, that there were around 100 acts of piracy in 2009 in the Gulf of Guinea," Morin said. "We are completely mobilised in Paris and Abuja to secure their release," foreign ministry spokesman Romain Nadal said, adding that Paris is in close "contact with the Nigerian authorities, Bourbon officials and the families." "I can confirm there was an attack and four people were taken. I can't confirm their nationalities," said Colonel Timothy Antigha, spokesman for the Nigerian military's Joint Task Force in the delta region. The firm has been the target of several attacks in the past two years in the Niger Delta oil-producing area. Nine Bourbon workers were taken hostage along with their ship in January last year and freed a few days later. In October 2008 another of its ships was seized by pirates off the Nigerian coast. Two French crew members of a Bourbon supply ship were kidnapped by armed men in August 2008 in a bar in the port of Onne, near Port Harcourt, Nigeria's oil capital. They were freed in September of the same year. Hundreds of people, mostly oil workers, have been kidnapped in the region since 2006.