LAS VEGAS, Nev. (AP) - A U.S. official says the Mandalay Bay hotel casino didn't notify police that gunshots had been fired inside the tower until after a gunman opened fire on the crowd outside at a country music festival.

The official, who was briefed by law enforcement, wasn't authorized to discuss the matter publicly and spoke to The Associated Press on condition of anonymity Thursday.

The disclosure means there was a delay of some six minutes in summoning police to the scene as the gunman began firing in the deadliest mass shooting in modern U.S. history.

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The hotel previous questioned the timeline released by police.

Two hotel employees had called for help and reported gunman Stephen Paddock sprayed a hallway with bullets and struck an unarmed security guard in the leg.

Police said Monday that was six minutes before Paddock opened fire on the crowd, killing 58 people and injuring nearly 500 others.

The corporate owner of the high-rise Las Vegas Strip casino from which a gunman unleashed the deadliest mass shooting in modern U.S. history is squeezing a disputed police timeline of the start of the massacre down to seconds.

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MGM Resorts International said in a statement that shots were fired into a music festival crowd "at the same time as, or within 40 seconds after" a security guard first reported by hotel dispatch radio that shots were fired.

The casino company says Las Vegas police accounts saying the casino security guard was wounded at 9:59 p.m. Oct. 1, and that gunfire out the hotel windows began 6 minutes later, are inaccurate.

The statement also says Las Vegas police and armed Mandalay Bay casino security officers were "in the building" when the guard reported the shooting and "immediately responded to the 32nd floor."