Militants in southern Nigeria have released six members of a group of nine foreign oil workers they have been holding hostage since 18 February.
A US worker was the first of the group to be released
Five of them - two Egyptians, two Thais and a Filipino - were taken to the office of the state governor. A US man was handed to journalists earlier.
Another two Americans and one Briton are still being held.
The militants have been demanding a greater share of the region's oil wealth for local Ijaw people.
Their attacks have led to a 20% drop in Nigeria's oil exports.
The group of nine are all employees of US oil services company Willbros. They were seized on a boat while laying a pipeline for Shell.
The six hostages were brought in to the town of Warri in two batches, following their release earlier on Wednesday.
Delta State governor James Ibori said he was "very pleased" that the six had been freed, but appealed to the group for the release of the remaining three.
"I want to tell them that there is no political gain for holding on to the remaining three... any longer," French news agency AFP quoted him as saying.
But the Movement for the Emancipation of the Niger Delta (Mend) said that the remaining captives would be held until the group's demands were met and threatened to step up attacks against the country's oil industry.
"We will commence with attacks in another area of the Niger Delta with an aim to ensuring the total discontinuation of export of onshore crude oil," the group said in a statement after releasing the US hostage.
The militants said they wanted a pledge from the government that it would not launch reprisal attacks and said it should release two prominent local leaders, the BBC's Alex Last in Warri reports.
The militants also demanded that the Shell comply with a recent Nigerian court order and pay $1.5bn (£858m) in compensation for pollution in the Niger Delta, our correspondent says.
The first hostage to be released, Macon Hawkins of Texas, said it felt great to be free.
His captors, armed with machine guns and rocket-propelled grenades, appeared out of the mangrove creeks to hand him over to journalists, including the BBC's Alex Last.
The militants said they released Mr Hawkins, 69, for humanitarian reasons.
"He was released on account of his age and poor health, with a stern warning not to return to the Niger Delta unless as a visitor," the group said.
"No ransom for him or any other hostage has been demanded or received," the statement said.