The main militant group in Nigeria's oil producing Niger Delta region has scoffed at an amnesty offer announced on Thursday by President Umaru Yar'Adua, describing it as "unrealistic". "Such an offer by a government known for its insincerity must first be given to those who are being held captive by the Nigerian state for the rest of us to take seriously," the Movement for the Emancipation of the Niger Delta (MEND) said in a statement e-mailed to journalists, in an apparent reference to its leader, Henry Okah, who is being tried for treason by the government.