Pirates boarded the Bourbon Liberty 249 off the coast of Nigeria and took hostage six Russians and one Estonian. Nine other crew members were unharmed and arrived safely in Onne, a Nigerian port.

The kidnapping occurred on Monday in the Gulf of Guinea, according to Reuters. The vessel was part of a fleet that the French company Bourbon leases to the offshore oil industry.

The kidnapping is just the latest in a series of recent attacks by pirates in the Gulf of Guinea, the  BBC reports. Bourbon says it has sent an "emergency unit" in hopes of bringing the seven hostages back safely.

No ransom demands have been reported. The Nigerian Navy is also looking for the pirates, notes Reuters.

This is not the first time pirates have targeted Bourbon, according to the BBC. In 2010, three French crewmembers were taken hostage by pirates in the Niger Delta although they were later released.  Normally, cargo, not crew, is the main target for pirates although crew could be held in exchange for money.

In August, a Greek fuel ship was captured in the Gulf of Guinea. Before releasing the ship, the pirates stole close to 3,000 tons of fuel. Just last week, another Greek fuel ship was hijacked on its way to the Ivory Coast port of Abidjan. No updates on the whereabouts of the ship or its 24 crew members have been reported.

The Gulf of Guinea has become a favorite among pirates, second only to the waters off Somalia for  number of piracy incidents.  The lucrative underground fuel trade has led to an increase in the number of pirate attacks, notes BBC.

According to the BBC, there have been 17 pirate attacks on ships in the waters surrounding Nigeria in 2012.