ONTARIO (CBSLA/AP) — Officials say two UPS employees were killed in a vehicle accident at the package-delivery service’s hub at Southern California’s Ontario International Airport.

UPS spokesman Steve Gaut said Monday’s accident involved two part-time package handlers. They have not been identified.

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The state’s workplace safety agency, known as Cal-OSHA, will investigate. Agency spokesman Luke Brown tells the Los Angeles Times the victims were on a tug — a tractor-like vehicle used to tow heavy shipments — when it flipped over.

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Additional details were not immediately available.

The facility underwent an expansion to double its sorting capacity in 2016, according to The Press-Enterprise.

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