Lagos, Nigeria ? An American worker held hostage in Nigeria is sick, and his kidnappers will kill three fellow hostages if he dies, a militant leader threatened Saturday.

Brutus Ebipadei, of the Movement for the Emancipation of the Niger Delta, did not offer details on the condition of Patrick Landry, a ship captain from Houston, or say why his group would kill hostages from Britain, Bulgaria and Honduras if he died.

“They’re drinking the bad water we’re drinking and experiencing the conditions our people have suffered for decades,” Ebipadei said.

If Landry dies, “we’ll have no choice but to kill the remaining ones,” Ebipadei said. He did not say why.

Ebipadei said the kidnappers refused to negotiate, and he reissued a threat to launch new attacks on installations in the oil-rich Niger Delta.

The militants demand the release of a former regional governor and a militant leader who pushed for greater local control of revenues from the delta. They also want $1.5 billion in compensation from Royal Dutch Shell, Nigeria’s largest oil producer, for alleged environmental damage.

Nigeria, Africa’s leading oil producer, exports about 2.5 million barrels of oil a day, making it the fifth-largest source of U.S. oil.