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At least three professional sports leagues warned their teams this week that organized and skilled groups are targeting the homes of athletes for break-ins, including while the players are away at games.

The warnings came after recent reports of burglaries at the homes of players in the NBA and the NFL – including Kansas City Chiefs stars Patrick Mahomes and Travis Kelce.

The NFL issued its security bulletin to teams Wednesday, advising that thieves “appear to exploit team schedules to target athletes’ homes on game days.”

The criminals are using several methods to figure out where professional athletes live and when they will be away from home – including public records, social media and news reports – along with their own surveillance of the properties, according to the bulletin.

The NHL told CNN Friday it also cautioned its teams about the burglaries, but it declined to share any communication it sent to clubs and the players union.

Here’s what we know:

The NFL memo does not provide details about the groups’ identities.

NBA league security officials, however, in a Thursday memo obtained by CNN, said they received an FBI briefing that connected many burglaries of athletes’ and high-net-worth peoples’ homes “to transnational South American Theft Groups.”

“These (South American Theft Groups) are reportedly well-organized, sophisticated rings that incorporate advanced techniques and technologies, including pre-surveillance, drones, and signal jamming devices,” the memo reads, as first reported by The Athletic.

“The FBI reported that, in most of the incidents, the homes were equipped with alarm systems that were not activated,” the NBA memo said. “The FBI also reported that the homes were all unoccupied and, in most cases, no dogs were present.”

The FBI declined to comment to CNN about the matter Thursday. But a source familiar with the investigation told CNN the FBI and local law enforcement agencies are working to determine whether the burglars are part of a transnational crime syndicate.

The leagues’ warnings came amid growing concern in recent months from law enforcement agencies over “burglary tourists.” Such criminals, authorities say, enter the United States from countries that qualify for visa waivers, allowing a visit of up to 90 days without a traditional tourist visa. When the would-be thieves arrive – most often from South America, prosecutors say – they join sophisticated burglary rings that prey on luxury homes.

The leagues’ memos do not spell out whether the groups they warn about precisely fit the concerns previously expressed by law enforcement agencies about burglary tourists.

Earlier this year, CNN spoke to a California couple whose home, prosecutors say, was broken into by burglary tourists. Carol and Jeff Starr said their family’s $8 million antique jewelry collection was taken from their Orange County residence.

Such thieves in some cases use camouflage suits to avoid detection, and can use WiFi jammers to disable alarm communications, county District Attorney Todd Spitzer told CNN for a story published in April.

What the NFL and the NBA are telling players

The NFL 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; storing valuable items out of plain sight; and using a trusted house sitter when possible.

The NBA memo also urged athletes to remove any real estate listings with interior photos of their home from publicly accessible websites, to use dogs for home protection, and to vet contractors doing any work in or around their home.

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

Thieves appear to be choosing the easiest targets: homes that were unoccupied with alarm systems that were not armed, the NBA memo says.

Joe Dumars, the NBA’s head of basketball operations, told CNN Friday the memo is meant to “remind people to be careful, to be vigilant and to be safe.”

“Nothing is more important than the safety of all of our key stakeholders throughout the NBA,” Dumars said.

Burglaries at the homes of Mahomes, Kelce, and other athletes

The Kansas City-area homes of Mahomes and Kelce were burglarized in October, CNN affiliates KCTV and KSHB reported.

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

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 Kelce’s, according to KCTV and KSHB. The police report indicated $20,000 in cash was stolen and $1,000 worth of damage was done to a rear door.

Mike Conley Jr., a guard for the NBA’s Minnesota Timberwolves, was at a Vikings football game on September 15 when thieves hit his home, the Minnesota Star Tribune reported. Jewelry was taken in the break-in, according to the newspaper.

Milwaukee Bucks player Bobby Portis said on social media his home was burglarized on November 2, and “they took most of my prized possessions.”

Mahomes spoke about the crime when a reporter interviewed him last week.

“Obviously, it’s frustrating, it’s disappointing,” Mahomes said. “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.”

Portis expressed his own anger on Instagram, saying he still wants to “uplift the community,” but was shocked to be a victim of a burglary. Portis also posted surveillance video showing two masked individuals appearing to use a tool to break a glass door at his home.

Kelce and Conley have not publicly commented on the thefts at their homes.

CNN’s Chris Boyette, Hanna Park and Andy Scholes contributed to this report.