U.S. police officers were told to be on high alert this week for Friday's anniversary of the Sept. 11, 2001, terror attacks, according to reports from conservative media. The alert was prompted by several death threats reportedly coming from activists associated with the Black Lives Matter social justice movement that has put a spotlight on police brutality. The seriousness of the alleged threats was unclear.

Several “Be On Look Out” warnings went out to state and municipal law enforcement agencies across the country this week, according to a report by the Daily Caller, a right-leaning news site. The outlet said it obtained several BOLO alerts indicating that members of Black Lives Matter and “#FYF911,” a group opposed to the American and Confederate battle flags, had called for the murder of police officers on Friday.

The alerts -- whose sources the Daily Caller did not identify -- come after highly publicized police officer gunfire deaths in California, Texas and Illinois in recent weeks. Law enforcement officials and conservative politicians have asserted that Black Lives Matter’s anti-police rhetoric has endangered the lives of policemen and women.

An Internet radio show purportedly tied to “black supremacy” and “black liberation” groups recorded a segment that included threats of violence toward police officers, the Daily Caller reported. One caller on the show said, “When those [expletive] are by themselves, that’s when we should start [expletive] them up.” That caller later said, “’Cause we already roll up in gangs anyway. There should be six or seven black [expletive], [who] see that white person, and then lynch their ass. Let’s turn the tables.”

One BOLO alert to police officers read: “The narrator known as ‘King Noble’ on Facebook states: ‘It’s open season on killing whites and police officers and probably killing cops period. It’s open season. Picking them off. Today we live in a time when the white man will be picked off.'”

Another BOLO alert calls for states to heighten security measures to protect officers from violence. "Law enforcement and military personnel should be extremely vigilant and take extra safety precautions on 9/11,” the BOLO read, according to the Daily Caller.

Although total line-of-duty deaths (which include traffic accidents and natural causes) are up this year compared to the same period last year, fatal shootings of officers are down, according to groups that track police deaths. At least 24 officers have died due to felonious gunfire this year, a website called the Officer Down Memorial Page reported Thursday.