Nigeria Sunday intensified its search for four foreigners kidnapped during a deadly attack on a vessel belonging to an oil services company, the navy said.

The suspected pirates stormed the vessel belonging to the Sea Trucks Group early Saturday in the Gulf of Guinea, an area that has seen a sharp spike in the number of reported maritime attacks over the past six months.

"We have intensified our search for the kidnappers and the abducted four foreigners," Nigerian navy spokesman Commodore Kabir Aliyu told AFP.

Another naval officer, who declined to be named because he has no authority to speak to reporters, said that the search for the foreigners has continued in the creeks and waterways in the region.

"We are leaving no stone unturned in our efforts to get back these four foreigners who were kidnapped aboard the vessel. We are redoubling our efforts," he said.

A spokeswoman for Sea Trucks Group, which provides support vessels to oil companies operating in Nigeria, said on Sunday that her company was focussed on the safe release of the hostages.

"We are very focussed on getting our crew back safely," Corrie van Kessel told AFP on telephone.

She declined to say categorically if contacts have been established with the abductors and efforts being made to secure their freedom, saying that releasing such information "could jeopardise current efforts."

Van Kessel confirmed that the four abducted foreigners were from Indonesia, Iran, Malaysia and Thailand.

Sea Trucks Group is heavily involved in the oil and gas sector in the Niger Delta.

The group, which also operates in Australia and East Asia, was founded as a Nigerian firm in 1977 before expanding and currently has a "corporate support office" in the Netherlands, according to its website.

Aliyu said during the attack "four expatriates are reported to have been kidnapped from the vessel; two sailors were killed."

Aliyu said six naval personnel were stationed on board the Sea Trucks Group vessel following a security request from the company.

The gunmen also shot and wounded two others while the remaining two escaped unhurt, he said.

The motive for the attack and the identities of the gunmen are still unknown, added Aliyu.

The attack took place before dawn on Saturday, 35 nautical miles off Nigeria's oil-rich Niger Delta coastal area, the navy and company said.

The volatile area was for years crippled by armed insurgency, largely made up of militants who claimed the region's prosperous oil industry was not benefitting the local population and destroying the environment.

Armed groups in the Delta were notorious for kidnapping oil workers, especially foreigners.

A 2009 amnesty deal greatly reduced the unrest, but sporadic incidents have continued to occur including robberies and, most prominently, piracy.

The International Maritime Bureau (IMB) said in a report released last month that there had been 32 piracy incidents recorded in the Gulf of Guinea in the first half of 2012, up from the 25 attacks in 2011.