OMAHA, Neb. (AP) — A 40-year-old Norfolk man has been sentenced for producing child pornography.

Federal prosecutors said Monday that Darrin Mucker was given 18 years in prison and must serve 20 years of supervised release after he leaves custody.

Prosecutors say Mucker posed as a teenager on a social networking service and sent obscene messages, including a sexually explicit image of a child. Mucker communicated with at least 15 girls ranging in age from 12 to 15 years. Mucker asked for and received images and videos from many of the girls engaged in sexually explicit conduct.

Prosecutors say that on at least one occasion he threatened to post on the Internet nude images he received of a 14-year-old girl unless she sent him more.