Eni said in a statement that the workers taken were an Australian, two Croatians, another from the UK, one from Romania and another from Poland.

They were working on the Mystras floating production, storage and offtake vessel, operated by Eni and Single Buoy Moorings, in an oil field 90km off the southern Nigerian coast.

But the kidnappers announced hours later that they had released their hostages

A report in the Age newspaper quoted a spokesperson from Australia’s Department of Foreign Affairs and Trade as saying the Australian High Commission in Abuja was liaising with local authorities regarding the safety and welfare of a 43-year-old.

“We understand that the people, including the Australian, have now been released, and apart from some bruising are reported as well,” the spokesman reportedly said.

Eni confirmed that the hostages had been released in a statement on its website.

“The workers seized this morning from the FPSO (Floating Production Storage and Offloading vessel) Mystras in Nigeria have all been released to the Chief Security Officer of the Rivers State.

“They are all reported to be in good health and will undertake all necessary medical check-ups shortly,” the company said.

The assault was one of three separate incidents in Nigeria yesterday, in which armed men abducted at least 20 foreigners.

It also comes two days after Nigerian militants launched a similar attack against Chevron, abducting six of the company’s foreign oil workers. Those workers are still being held. Chevron was forced to shut down 15,000 barrels a day of production due to the attack.