The Hague - Niger Delta gunmen have released two Nigerians they kidnapped two days ago, but kept three Dutch nationals who were abducted at the same time, one of those freed tweeted on Tuesday.

Environmental activist Sunny Ofehe tweeted that he and another kidnap victim were “released in the creek of Niger Delta last night by gunmen! The other 3 colleagues are yet to be freed.”

In a statement released later in Nigeria, the Amsterdam-based Nigerian activist Ofehe said the group was seized after armed men in a dinghy approached their boat, shooting “sporadically into the air.”

The gunmen yelled “Keep your faces down, if you make a single sound, we will shoot you,” Ofehe said.

The militants were looking specifically for the Dutch nationals, yelling “we want the white men” before taking the trio away separately on a dinghy.

Ofehe said three Dutch nationals, two men and a woman, were kidnapped in Nigeria's oil producing region while returning from inspecting a hospital built by US oil giant Chevron.

Dutch and Nigerian authorities confirmed the kidnapping.

Ofehe said he and another Netherlands-based Nigerian were also abducted.

They were blindfolded and eventually taken to an unknown location where they were later abandoned.

Before the kidnappers released them, they told “us to leave the Niger Delta region if we want to remain alive.”

“I appeal to the kidnappers to please release the other members of my team,” Ofehe said.

Scores of foreigners have been abducted in the southern Niger Delta region, home to Africa's largest oil industry, with many released on payment of a ransom.

The gunmen told Ofehe that “they were doing it for the money, that they didn't have jobs, that the oil companies active in the region were not hiring locals and as a consequence, they were forced to do this.”

Nigeria police told AFP in Lagos that the kidnappers had made a ransom demand for Ofehe, but it was not clear if his release was linked to any payment.

“The kidnappers contacted the family of the Nigerian man that was seized with the Dutch nationals and asked for a 10 million naira ransom ($60 000, 43 000 euros),” Bayelsa state police spokesman Alex Akhigbe said.

“The police are not involved in ransom negotiations because we don't pay ransom to criminals,” he added.

Employees of foreign oil companies are required to have an armed escort when travelling in the Delta, but international journalists, aid workers and others typically avoid taking a security detail.

Dutch printing company Gerrits&Leffers said on Monday that two of its employees were among those abducted and that the pair were in Nigeria to help Niger Delta peace activists publish a magazine.

Anglo-Dutch oil giant Shell has had a major presence in the region for decades, with its operations criticised over environmental degradation and close collaboration with the military dictators who led Nigeria through much of the 1980s and 1990s.

The delta, which churns out roughly two million barrels of crude each day, has seen years of unrest.

The violence eased after a 2009 amnesty deal with rebels in the region.

But crime remains widespread, including massive oil theft and ransom kidnappings.

The Niger Delta amnesty programme, which is set to expire in 2015, included massive payouts to militant leaders.

Analysts have voiced concern over worsening unrest in the region if the government does not pledge to extend the payouts. - Sapa-AFP