Leaflets demanding that Jews in eastern Ukraine must register with a "local-authority" or face consequences have been condemned as "grotesque" by the United States on Thursday, according to CNN.

U.S. officials said the anti-Semitic leaflets, which recall the days of czarist pogroms and Nazi-era persecution of Jews, have appeared recently in the eastern Ukrainian city of Donetsk, CNN reported. The State Department said it was looking into who is responsible but said it took the threat seriously no matter who was behind the leaflets.

The leaflets reportedly come from the Donetsk People's Republic, a self-styled, unrecognized breakaway authority that seeks to join Russia, CNN reported. The Donetsk Republic press office denied any involvement in the matter and says the leaflets are fake.

Top U.S. officials also denounced other instances of religious intolerance that are inflaming tensions the crisis in Ukraine and said no such behavior could be tolerated, CNN reported.

Secretary of State John Kerry denounced the leaflets after speaking with top diplomats from the U.S., European Union, Russia and Ukraine in Geneva as they reached an agreement on steps to de-escalate the situation in Ukraine, according to CNN.

"In the year 2014, after all of the miles traveled and all of the journey of history, this is not just intolerable; it's grotesque," Kerry told reporters, CNN reported. "It is beyond unacceptable. And any of the people who engage in these kinds of activities, from whatever party or whatever ideology or whatever place they crawl out of, there is no place for that. "

Kerry also denounced apparent threats to members of the Russian Orthodox Church from members of the Ukrainian Orthodox Church, according to CNN.

Kerry also touched on the agreement signed on Thursday "strongly condemned and rejected all expressions of extremism, racism and religious intolerance, including anti-Semitism," CNN reported.