There’s been a spree of armed robberies on traveling jewelry salesmen in the Houston area that authorities say has cost victims $3 million in stolen valuables, The Associated Press reports.

The fourth holdup in three weeks happened Thursday afternoon when police say three masked men walked into a Waffle House, went straight for a dealer seated in a corner booth, pistol-whipped him, and made off with $1.4 million in diamonds, the AP reports.

Steven Silver, who works for the Texas Jewelers Security Hotline, told the AP that the city is fast getting a reputation as a city for traveling dealers to avoid. In some cases, he said, insurance companies won’t allow salespersons to go into the area.

FBI agents believe the robbers are part of a larger ring of South American thieves, which has operated in United States for at least 20 years, the AP reports.

The spree in Houston began April 28 when authorities say four men in a hotel parking lot jumped a New York salesman, pulling the man from his car and stealing $600,000 worth of merchandise, the AP reports.

Days later, another dealer was sitting inside his car when police say three robbers teamed up to smash the driver’s side window, slash the tires and pin down the driver while $250,000 in precious stones were taken from the trunk.

And on Wednesday, authorities say robbers took $1 million in jewelry and gems from a dealer who stopped for gas late in the afternoon.

FBI agents said they’re doing everything they can to track down the robbers, but admit the challenge is daunting, the AP reports.

Authorities also reportedly said that they believe the same ring of robbers committed a robberies I the Houston area in 2003.

JCK