A jewelry salesman was stabbed and robbed of 600 carats in diamonds on Tuesday outside of a southeast Houston gas station, the Houston Chronicle reports.

It was sixth such robbery in Houston since April, the newspaper reports. Authorities believe it is the work of South American theft gangs.

Five men with wielding knives and at least one pistol jumped the dealer soon after he pulled into the gas station at about 3:30 p.m., police reportedly said. The thieves forced the salesman to the ground and stabbed him in his right arm.

The robbers went back to the man’s car and took his briefcase, which held the diamonds, officials reportedly said. The victim was treated and released at a local hospital and has returned home to California.

The value of the diamonds were not released, the newspaper reports. No arrests have been made.

Investigators reportedly said they believe Tuesday’s hold-up was committed by members of a violent South American gang targeting jewelry dealers traveling in the Houston area. At least five similar holdups, netting the gang more than $3.5 million, have occurred since late April.

JCK