SAN DIEGO (NEWS 8/CNS) - An investigation was underway Monday into the cause of a sudden, intense fire at MCAS Miramar, where two Marines suffered severe burn injuries. 

The two Marines from Texas-based reserve unit Marine Fighter Attack Squadron 112, also known as the "Cowboys," were working on a F/A-18 Hornet jet when the flash fire ignited on the ground around 10:20 p.m. Sunday, according to Maj. Kurt Stahl, Miramar's public affairs director. 

The fire appeared like an explosion and badly burned the two Marines.  

"They were performing routine aircraft maintenance on an F-18 at the time," said Public Affairs Officer Major Andrew Aranda. "Both Marines are currently being treated for severe burns at UC San Diego Regional Burn Center." 

No other marines were injured from the fire. 

The Marines from Texas were in San Diego for their annual reserve training. 

Their squadron was the last fighter/attack squadron to leave Iraq closing that chapter on the Iraq War. 

And in 2004, the "Cowboys" were the first reserve squadron to deploy to the Western Pacific since the Korean War. 

It's still unclear how the flash fire initially sparked or if heat or aircraft fuel had anything to do with it. 

The case is now under investigation and transferred from MCAS Miramar over to the Marine Forces Reserve. 

"We're looking into everything, all the contributing causes, because this is obviously a very serious incident, and we want to make sure we figure out exactly what happened; and make sure something like that doesn't happen again," said Aranda. 

The Marine Reserves say they will update the condition of the injured marines as soon as they receive word from doctors. 

"Our thoughts and prayers go out to their friends and families right now through this difficult time," Aranda said.