The kidnapped German contractor, whose identity has not been officially released, is "doing well" considering the circumstances, according to Herbert Bodner, chairman of Germany's Bilfinger Berger construction company, which employed the kidnapped man for the last 18 years.

Without giving additional details, Bodner said the company had been in contact with the kidnappers multiple times and that everything had been done to ensure the man's safe release.

Originally from the Bavarian city of Würzburg, the hostage said he was "alive and well," but wanted to go home, according to an e-mail released to the media on Wednesday.

"So far I have been treated well by my captors," the German man, a contractor for the Bilfinger Berger construction company. "They have provided me with mosquito nets. They have also provided me with medicines and even brought me a packet of my favorite cigarette."

The German Foreign Ministry would not confirm knowledge of the photo or the man's identity, but said its crisis response team has been in contact with the Nigerian authorities with the goal of achieving "the quickest release possible," according to a spokesman on Wednesday.

The militants holding him after his kidnapping a week ago from Port Harcourt demanded the release of two ethnic Ijaw leaders being held prisoner as well as added jobs and investment in the Niger Delta region by the German captive's employer.

"We are still waiting for our demands to be met," the kidnappers said in a previous statement.

Mujahid Dokubo Asari, one of the men the previously unknown Movement for the Niger Delta People (MONDP) wants released, appealed for the German hostage to be set free.

"Asari wishes to appeal to the kidnappers to release unconditionally their hostage as he has no hand in his travails," according to a statement issued by Allen Onyema, one of Asari's associates.

Onyema added that although Asari appreciated the concern of the militants for his plight, he would prefer a peaceful means to resolve the crisis, Onyema added.

Five additional Europeans kidnapped

The past seven months have seen a wave of kidnappings and attacks on oil facilities and personnel by separatist agitators in the Niger Delta, home to Nigeria's multi-billion-dollar oil and gas wealth. Rebels have often demanded a larger share of the country's profits from natural resources be returned to the public.

Most recently, a Belgian and Moroccan were kidnapped Thursday, and two Norwegians and two Ukrainians were kidnapped at gunpoint from an oil services ship off the coast of Nigeria on Wednesday, and three Filipino workers were kidnapped last week in an incident separate from the German hostage taking.

Nigeria is Africa's biggest producer and the eighth largest in the world, accounting for a daily output of 2.6 million barrels, but unrest has cut a quarter of that figure in recent months.