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BUCHAREST, Romania — Officials say 12 U.S. paratroopers have been hospitalized after they sustained minor injuries during a nighttime parachute jump in Romania.

Paratroopers prepare for a jump while onboard an US C-17 Globemaster III military transport aircraft flying in Bulgaria's airspace, during the Swift Response 2017 international military exercise on July 19, 2017. The U.S. Army Europe led the 'Swift Response 17' airborne exercise, as a part of the Saber Guardian 2017 (SG17) multinational military exercise which takes place in numerous locations across Bulgaria, Hungary and Romania in the summer of 2017, involving up to 45,000 soldiers from North Atlantic Treaty Organization (NATO) countries. Csaba Krizsan / EPA

Brent M. William, a spokesman for the "Atlantic Resolve" military exercises, told Romania's Agerpres news agency the accident occurred early Saturday at the Campia Turzii air base in northwest Romania. He said 500 troops jumped from C-130 Hercules planes during "a very rigorous exercise, which carries a certain level of risk."

The Cluj Military Hospital spokeswoman, Doina Baltaru, said 11 soldiers were discharged Sunday from the hospital. She said one other soldier suffered a bruised spine and would remain hospitalized up to two more days.

The soldiers were participating in Saber Guardian 17, a U.S. Army Europe-led exercise, which aims to increase coordination between the U.S., Bulgaria, Hungary and Romania.