HEIDELBERG — Monkeys being transported on a Mississippi highway escaped captivity Tuesday after the truck carrying them overturned, according to law enforcement.

All but one of the escaped monkeys were killed, the Jasper County Sheriff’s Department said in a post on Facebook, warning that the monkeys were “aggressive.” It is not clear how many monkeys were originally in the truck.

The truck was carrying Rhesus monkeys, which typically weigh around 16 pounds and are among the most medically studied animals on the planet. They were being housed at the Tulane University National Biomedical Research Center in New Orleans, Louisiana, which routinely provides primates to scientific research organizations, according to the university.

It is not clear who was transporting the monkeys or where they were being taken.

Video shows monkeys crawling through tall grass on the side of Interstate 59 just north of Heidelberg, Mississippi, with wooden crates labeled “live animals” crumpled and strewn about.

The sheriff’s department initially said the monkeys were carrying diseases including herpes, but Tulane University said in a statement that the monkeys “are not infectious.” The sheriff’s department responded by saying the driver of the truck told law enforcement the monkeys were dangerous and needed to be handled using personal protective equipment.

Tulane University said it is working with law enforcement. Mississippi Wildlife and Fisheries was also on site.

The crash happened about 100 miles from the state capital of Jackson. It is not clear what caused the truck to overturn.