The leader of Nigerian militants who captured four foreign oil workers has said he would not talk with negotiators sent by the government and reiterated threats to launch new attacks on oil installations.
Brutus Ebipadei, a leader of the Movement for the Emancipation of the Niger Delta, also said on Saturday that US hostage Patrick Landry is sick and warned that if he dies, his group would kill the remaining hostages.
He did not say why the other hostages would be killed and it was not possible to independently confirm the state of Landry's health.
Ebipadei has claimed responsibility for a spate of attacks on oil installations in Nigeria that included the kidnapping of four foreigners -- Landry, a Briton, a Bulgarian and a Honduran -- from a Shell oil platform last week.
Ebipadei is also demanding the release of two imprisoned figureheads of his ethnic Ijaw group.
"Our demands are not negotiable. And failure to meet those demands means we will launch attacks on all oil installations to stop Nigeria's capacity to export oil," Ebipadei said by telephone from an undisclosed location.
"We are not going to say when we will attack, but it's going to be any moment from now," Ebipadei said.
The workers were seized on Jan. 11 near a Shell oil field by militants behind attacks on Nigerian oil installations that have cut the OPEC-member nation's crude output by nearly 10 percent.
A major Shell pipeline leading to its Forcados export terminal was blown up the following day, and more attacks followed in other areas.
Shell has evacuated hundreds of workers from the delta since the unrest began.
Ebipadei said negotiators sent by the government to secure the hostages' release "are traitors to the Ijaw cause and we're not ready to deal with them."
The militia leader's hardline stance contrasted with the optimism expressed by the country's officials.
"Negotiations are going on and they have reached a very good level," Bayelsa government spokesman Ekiyor Welson said. "With God's grace ... they will soon be released."
Asked why he felt optimistic, Welson said: "People are pleading with them, and the pleas are beginning to reach them."
It was not known where the hostages were being held, but Ebipadei said: "The hostages are with us. They're drinking the bad water we're drinking and experiencing the conditions our people have suffered for decades."
He added that if Landry dies "we'll have no choice but to kill the remaining ones."
On Friday, the US State Department called for the release of the four captives, while a British diplomat said his country was pressing Nigeria not to use force to free them.
The militants are demanding the release of militia leader Mujahid Dokubo-Asari and the former governor of Bayelsa, Diepreye Alamieyeseigha.