A Canadian oil worker is among at least five people who were abducted during an attack on an oil rig off southern Nigeria early Monday morning, officials confirm.

The workers were kidnapped by a group of gunmen in speedboats, who attacked a new rig operated by London-based Afren PLC. The rig was surveying at the Okoro oilfield, which is located about 11 kilometres off the coast of Nigeria's Akwa Ibom state.

A spokesperson for Afren confirmed that a Canadian was among those kidnapped, but would not offer more information. The other kidnapped workers are French and American.

Family members confirmed to The Canadian Press late Monday that the Canadian hostage is Bob Croke, who is from the St. John's, N.L. area.

Lisa Monette, a spokesperson for the Department of Foreign Affairs, would only say that the government is aware of reports that a Canadian national is missing in Nigeria.

"The Department of Foreign Affairs and International Trade is in touch with local authorities with a view to seeking further information," Monette told CTV.ca in an email. "Due to the Privacy Act, no additional information can be released at this time."

Some of those kidnapped were employees of drilling company Transocean, which is now on a heightened state of alert and has increased security on its other rigs near Nigeria.

"All I can tell you is we are working with our customer Afren and the authorities. We have not been contacted by the perpetrators," company spokesperson Guy Cantwell told The Canadian Press from Houston.

While early reports suggested that five people had been kidnapped, the U.S. State Department put the number at seven, including two Americans.

"We, of course, (are) concerned about their safety and hope for their immediate return," Crowley told reporters. "We are working with Nigerian authorities ... to pursue their prompt release."

It was unclear late Monday why there is a discrepancy in the number of workers who are believed to have been kidnapped. Earlier in the day, Afren had revealed that five people had been taken hostage and that two other workers were injured in the attack. They suffered leg wounds and were flown from the rig by helicopter for medical treatment.

"We are working with the relevant authorities and the vessel and rig are both under the control of the company," Afren said in a statement. "Drilling operations on the rig are temporarily suspended. An update will be provided in due course."

Attacks on rigs across the Niger Delta began in 2006, as a way for militants to protest pollution from offshore operations, as well as high poverty rates among local populations that were not sharing in the oil profits.

Violence subsided last year after the government introduced an amnesty program, through which militants were offered money and job training. However, not all militants chose to participate in the program.

No group claimed responsibility for Monday's attack. However, one of the region's main militant groups, the Movement for the Emancipation of the Niger Delta, had previously said it would step up attacks in the region. It last claimed responsibility for a car bombing in the capital of Abuja on Oct. 1 that killed 12 people and injured dozens of others.

An email message purporting to be from the group circulated Monday, saying the group would launch more attacks on oil rigs across the Niger Delta. However, that message came from an email address not known to be linked to the group.

Nigeria's navy often provides security for offshore operations, but there were no ships near the Afren rig on Monday when the attack occurred.

Navy spokesperson Capt. Kabir Aliyu, said two boats arrived on scene in time to shoot at the attackers as they left the scene.

Afren conducts operations in the Okoro field in conjunction with private Nigerian firm Amni International. The company is exploring eight oil fields in Nigeria with local partner companies.

The company has said the Okoro field produces about 18,800 barrels of oil per day and has an estimated reserve of 24.8 million barrels.

With files from The Canadian Press and The Associated Press