UPDATED: 14 Marines and one Navy corpsman were injured in the accident.

Six of the 15 service members injured Wednesday when their Marine amphibious assault vehicle caught fire are in critical condition, Corps officials said.

The 14 Marines and one sailor are from 1st Battalion, 1st Marines and the 3rd Assault Amphibian Battalion, said 1st Lt. Paul Gainey, a spokesman for the 1st Marine Division. They were conducting a combat readiness evaluation as part of a training exercise at Camp Pendleton, California, when the AAV burst into flames at 9:33 a.m. local time.

Eight of the service members were sent to the Burn Center at University of California San Diego Health, where three are listed in critical condition and five are in serious condition, Gainey said in a news release.

Four other service members were taken to the University of California Irvine Medical Center, where three of them are listed in critical condition and one is in serious condition, the 1st Marine Division tweeted on Wednesday.

UPDATE (1/2): Of the two Marines previously listed in unknown condition, one Marine is in critical condition and one is in serious condition — 1st Marine Division (@1st_Marine_Div) September 14, 2017

Another service member is listed in stable condition at Scripps Memorial Hospital La Jolla, California; and two service members are being treated for minor injuries at Naval Hospital Camp Pendleton, Gainey said.

“The 1st Marine Division would like to thank the civilian and military emergency personnel who responded immediately to the situation and allowed the injured Marines to receive rapid care,” Gainey said. “Our thoughts and prayers are with the Marines and their families affected by this incident.”

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The accident is under investigation. Business Insider first reported the incident on Wednesday.

Wednesday’s incident is the Marine Corps’ third major training accident in as many months: Three Marines were killed on Aug. 5 when an MV-22B Osprey crashed off Australia; and 15 Marines and one sailor were killed on July 10 when their KC-130T crashed in Mississippi.

The two fatal crashes led Marine Commandant Robert Neller on Aug. 12 to order all Marine squadrons to suspend flight operations for 24 hours. Sen. John McCain, R-Ariz., called the pause in flight operations, “the latest example of the readiness crisis that threatens to cripple the U.S. military’s advantage over our adversaries.”