Three mosques in Southern California are on edge after receiving threatening letters last week.
Targeted mosques include the Long Beach Islamic Center, the Islamic Center of Claremont and a mosque in the San Fernando Valley.
Tarek Mohamed, chairman of the Long Beach Islamic Center, tells KPCC some of the things the letter said: "Calling the Muslim community and Muslims in general the son of Satan, and you need to pack up your luggage and leave the country, and nobody can protect you from us."
According to Hussam Ayloush, executive director of the Council on American Islamic Relations for greater Los Angeles, the letters all appear to have been sent by the same person. The sender wrote separate fake names and fake addresses on each letter but all were postmarked in Santa Clarita.
CAIR says it has seen a spike in incidents targeting Muslim Americans since the presidential election.
"It's not unusual. We've had these kind of letters before," Ayloush tells KPCC. "What is unusual is... the fact that it was more than one mosque."
A fourth mosque in Northern California, the Evergreen Islamic Center in San Jose, also received the letter.
CAIR posted a photo of the letter on its Facebook page. The letter was addressed to "the children of Satan" and it was signed by "Americans for A Better Way."
In part, it reads: "There's a new sheriff in town — President Donald Trump. He's going to cleanse America and make it shine again. And, he's going to start with you Muslims. He's going to do to you Muslims what Hitler did to the jews (sic)."
"What we don't know is how serious is this person about their hatred? Is it merely someone venting their hatred on Muslims or is it something that person might be planning to take action?" Ayloush says.
CAIR is calling on local law enforcement and the FBI to get involved in an investigation.
Ayloush says: "Members in the Muslim community, they're very disheartened to know that there are people out there, as small as a number as that might be, who are so angry, so hateful and so ignorant toward fellow Americans just because they share a different faith."