A registered sex offender was ordered detained in federal custody Wednesday on charges of possessing child pornography, less than five months after he had completed a prison sentence that followed his conviction on a similar charge.

According to a news release from the office of U.S. Attorney Stephen G. Dambruch, a U.S. probation officer found inappropriate materials on a cellphone belonging to Robert L. MacGregor, 55, of Providence, during a routine home visit on Jan. 24. A subsequent forensic examination of the phone revealed about 100 images of child pornography, according to the news release.

MacGregor was on lifetime supervised release following a 2011 conviction for possessing and distributing child pornography.

If convicted of the second offense, MacGregor faces a mandatory minimum sentence of 10 years in prison, with a maximum of 20 years, as well as lifetime supervised release and a fine of up to $250,000.