The NFL issued a security alert to team security directors and the players’ union Wednesday about organized and skilled criminals that are increasingly targeting the homes of professional athletes, including the recent burglaries of Kansas City Chiefs stars Patrick Mahomes and Travis Kelce, according to the memo obtained by NFL.com.

Sources say the FBI is investigating the crime wave as international organized crime. The league, the NFL Players Association and team security forces also have been monitoring the crime spree, which is believed to be tied to a South American crime syndicate. At least one other current NFL player’s home was burglarized in the past week.

“It’s legit,” said one source familiar with the situation. “It’s a transnational crime ring, and over the last three weeks, they’ve focused on NBA and NFL players, and it’s all over the country.”

Citing longstanding Department of Justice policy, a spokesperson for the FBI Office of Public Affairs declined to confirm or deny the existence of an investigation and had no further comment.

The homes of Mahomes and Kelce were burglarized on consecutive days last month in the Kansas City area. The Minnesota home of former Vikings defensive tackle Linval Joseph, who now plays for the Dallas Cowboys, was part of a series of burglaries last weekend, according to police.

Multiple people with knowledge of the crimes said the perpetrators are nonconfrontational and do not burglarize homes while residents are inside. Instead, they use public records to find players’ addresses and conduct extensive surveillance. Then, by tracking team schedules and the social media accounts of players and their families, they wait until homes are empty — often during games — and gain access and quickly steal items such as cash, jewelry, watches and handbags, focusing mainly on master bedrooms and closets.

The alert issued on Wednesday by NFL Security confirmed the modus operandi and offered a number of recommendations, including not posting in real time on social media, installing security systems and keeping valuables out of plain sight.