JERUSALEM — The world’s predominant Nazi-hunting group took the United States to task Monday over its failure to prosecute a member of a notorious Nazi unit who lived quietly in Minnesota for decades.

The Simon Wiesenthal Center’s annual report lowered its ranking of the United States’ Nazi-hunting efforts from A to B. It was the first time the nation has been ranked so low.

Efraim Zuroff, director of the center’s Israel office, said the ranking was in part because the United States took no action against Michael Karkoc.

An Associated Press investigation in 2013 found that Karkoc, a commander of a Nazi SS-led unit accused of atrocities, has been living in Minnesota since shortly after World War II.

A German investigation began after the AP published the story establishing that Karkoc commanded a unit accused of burning villages filled with women and children, then lied to immigration officials to get into the United States.

This year’s report praised Germany for loosening criteria to make it easier to prosecute former Nazis. For decades, prosecutors could only go after those suspected of specific involvement in specific atrocities. Now anyone who served in a death camp or a mobile killing squad during World War II can be prosecuted as accessories to murder.

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