LOS ANGELES — Ever since the Trump immigration raids began in Los Angeles in June, local leaders and community activists have criticized agents for sometimes making it difficult to identify them as federal law enforcement officials or refusing to identify themselves at all.

Now, an unexpected new group has expressed its own concerns: the FBI. Citing a string of incidents in which masked criminals posing as immigration officers robbed and kidnapped victims, the FBI recently issued a memo suggesting agents clearly identify themselves while they’re in the field.

The FBI explained its reasoning in a three-page document sent to police agencies across the country last month.

In the memo, the FBI says criminals impersonating law enforcement “damages trust” between them and the community and that law enforcement has an “opportunity” to better coordinate with their local, state and federal partners, carry out informational campaigns to educate the public about impostors and for agents to show their identification when asked while out in the field.

Undocumented immigrants and U.S. citizens have been detained by masked people on city streets, in hospitals, courthouses, and outside schools and places of worship over the last several months. California has banned the use of masks among law enforcement agencies, but on Tuesday a cadre of masked agents gathered in an offsite Dodger Stadium parking lot while carrying out more raids.

The FBI’s memo, obtained through a records request by the national security transparency nonprofit Property of the People, was prepared by the New York field office and first reported by Wired magazine. It details several instances where people impersonated immigration agents.

The FBI’s national press office did not respond to requests for comment, citing the government shutdown in an automated email response.