"We find ourselves in a more dangerous situation," an outgoing counter-terror chief said.
The maintenance worker told hotel dispatchers to call police to report a gunman had opened fire.
The "person of interest" in the investigation has flown back to the U.S. to be interviewed by federal agents.
The group said that Stephen Paddock was one of its "soldiers" after the mass shooting.
The jihadi group said the attacker was inspired by its calls to target "coalition" countries.
The attack killed at least 58 people and injured 500 more.
The 2015 footage, posted by the group in May, showed the strip alongside New York and Washington, D.C.
The group wants jihadists in the west to inject cyanide poison into supermarket goods.
Senior envoy says president handed greater control to commanders to get the job done.
The 21-year-old also wanted to commit an attack for what he called the "Islamic State of North Carolina."
The president's campaign against ISIS is killing 12 civilians a day, new investigation shows.
He called the mounting civilian casualties "a fact of life in this sort of situation."
Dabiq figures prominently in ISIS propaganda as the site of a future battle between Muslims and infidels that will presage doomsday.
Even if ISIS is crushed, any celebration should be short-lived.
Islamic State-held village is heralded as the setting for a final battle between Muslims and infidels.
The group's new issue of Dabiq magazine contains a picture of the soldier's tombstone.
Photos in propaganda magazine shows device allegedly stashed in a drinks can
The new release of ISIS's propaganda magazine publishes photos purporting to be bodies of hostages.
The terror group write about Boko Haram, Libya and Tunisia in the new publication of Dabiq.
Reports had claimed that ISIS planned to launch a 24-hour propaganda channel.