OMAHA, Neb. (AP) — An anti-defamation group says it's received hundreds of calls from Omaha residents upset over neo-Nazi books left in several Little Free Libraries.

Dozens of neo-Nazi books were found in outdoor book exchanges across Omaha, according to the Plains States Region of the Anti-Defamation League. The group said it's working with law enforcement to combat the rise in hate speech.

"This is a growing tactic used by white supremacists to get their message out," said Mary-Beth Muskin, the group's regional director. "Clearly, it is the act of one person or a few individuals."

The libraries are intended to bring the community together, said Susie Dugan, president of the Trendwood Neighborhood Association.

"It's a shame that something like this has to get hijacked by someone who is up to no good," Dugan said. "This is not what we are about. We are about helping each other, promoting neighborliness and safety."

Muskin said the activity isn't illegal but it's concerning.

"It's immoral and it's improper," she said. "The way we deal with these things is we stand up and say, 'It's not right.'"

Little Free Library owners will continue to sort through materials and throw out inappropriate literature, Muskin said.

Signs encouraging citizens to report individuals living in the country illegally have also turned up on poles in Omaha neighborhoods. Residents have been taking them down.

Resident Dalila Rios said the signs are discriminatory and invite people to make false assumptions.

Muskin said the signs send the wrong message to the area.

"Any time you are targeting a group and having the general public decide the citizenship of another person, it's concerning," she said. "It's not welcoming or civil."

The Anti-Defamation League urges any residents who encounter such propaganda to report it.