(CNN) — After recent burglaries at homes of professional athletes – including Kansas City Chiefs stars Patrick Mahomes and Travis Kelce – the NFL has issued a security bulletin to teams and the players union warning that “organized and skilled groups” are increasingly targeting players’ residences for such crimes.

The memo, issued Wednesday and obtained by CNN, warns that players across multiple sports leagues are being targeted. Perpetrators “appear to exploit team schedules to target athletes’ homes on game days,” and appear to be using public records, social media, media reports and surveillance to gather information on their targets, it says.

The memo recommends that players take certain social media precautions, including not posting activities as they happen, and not posting photos of high-dollar objects such as jewelry, watches or flashy clothing.

It also encourages players to take home security steps, including installing comprehensive systems with cameras, sensors and exterior lights; having solid exterior doors with deadbolt locks and reinforced frames; storing valuable items out of plain sight; and using a trusted house sitter when possible.

“It is important for players to maintain situational awareness, practice social media safety, and implement home security measures to reduce the risk of becoming a target,” the memo reads.

The memo does not provide details about the groups’ identities or give examples of specific burglaries. Local law enforcement and the FBI are working to identify the perpetrators and determine whether group members were part of a transnational crime syndicate, a source familiar with the investigation told CNN. The FBI on Thursday declined to comment to CNN.

Some groups, the NFL memo says, conduct extensive surveillance, including by making “attempted home deliveries” and “posing as grounds maintenance or joggers in a neighborhood.”

The Kansas City-area homes of Mahomes and Kelce were burglarized last month, according to local news outlets citing authorities.

One burglary happened early October 6 at a home in Missouri’s Cass County, a report from the county sheriff’s office said. That home belongs to Mahomes, the Chiefs’ quarterback, CNN affiliates KCTV and KSHB reported. Details about what was taken weren’t released.

“Obviously, it’s frustrating, it’s disappointing,” Mahomes said last week when asked about the burglary. “I can’t get into too many of the details because the investigation is still ongoing, but (it’s) obviously something that you don’t want to happen to really anybody but obviously yourself.”

The other burglary happened in eastern Kansas on the evening of October 7, according to a police report obtained by CNN – around the time the Chiefs were hosting the New Orleans Saints for a game aired on “Monday Night Football.” The home was believed to belong to Kelce, KCTV reported. The report, made to police on October 8, indicated $20,000 in cash was stolen and $1,000 worth of damage was done to a rear door.

CNN has reached out to both players and the Chiefs for comment.

Burglaries reported at NBA players’ homes

Reports of burglaries at the homes of NBA players have also recently emerged.

The home of Minnesota Timberwolves guard Mike Conley Jr. was burglarized on September 15 while he was attending a Minnesota Vikings game, the Minnesota Star Tribune reported. A “yet-to-be determined amount of jewelry” was stolen, the newspaper reported.

CNN has reached out to Conley, the Timberwolves and police in Medina, Minnesota, for more information and comment.

In an Instagram post on November 3, Milwaukee Bucks forward Bobby Portis said his home had been broken into the night before while he was playing in the Bucks’ home game against the Cleveland Cavaliers.

River Hills, Wisconsin, police have not yet responded to CNN’s request for details about the crime.

“Many of my prized possessions were stolen,” Portis said, and later offered a $40,000 reward for information directly leading to the return of the stolen items.

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