Terrorism experts said Monday they are not surprised ISIS would claim to be linked to the Nevada shooting since it fits a recent pattern of the terrorist group trying to claim credit for high-profile incidents.

"It seems like they're desperate for attention and will claim just about everything," said Colin Clarke, a Pittsburgh-based political scientist and terrorism expert for the think tank Rand Corporation. "They've lost so much territory, and they fear they're becoming irrelevant."

ISIS, or Islamic State of Iraq and Syria, claimed responsibility for the Las Vegas attack on an outdoor music festival and said accused shooter Stephen Paddock, 64, had converted to Islam months ago, according to the Amaq News Agency, an outlet linked to ISIS. Amaq didn't offer any evidence.

The shooting killed 58 people and left hundreds of others injured. It is the deadliest mass shooting in U.S. history.

The FBI said Monday the suspect in the deadly Las Vegas shooting doesn't appear to be connected to ISIS. The terror group also is sometimes referred to as ISIL, or Islamic State of Iraq and the Levant.

"We have determined to this point no connection with any international terror group," Aaron Rouse, special agent in charge of the FBI's field office in Las Vegas, told reporters. He indicated the agency would "continue to investigate."

Even so, Clarke noted that ISIS did call for attacks on the Las Vegas Strip several months ago. "This would play into their narrative, even though if you look at the demographic of the shooter ... it seems like a stretch to say he was a solider of the caliphate."

Experts say since losing Mosul, the second-largest city in Iraq, ISIS has claimed responsibility for several incidents it had nothing to do with, including an indebted gambler killing 37 people at a Manila casino in June and a false report last month of smuggled explosives at a Paris airport.

"We've seen them over the last year, as they start to lose territory, in Raqqa and Mosul, turn more and more towards internet radicalization, trying to claim credit for lone-wolf attacks," said Jasmine El-Gamal, a Beirut-based senior fellow at the Atlantic Council, a foreign policy think tank. "So it's completely unsurprising to me that they try to claim credit for this, but there's no proof of it so far."

"What it does is that just brings them more media attention, which at the end of the day is what they need more than ever now that they don't have their physical caliphate," El-Gamal added.

On Monday, the Defense Department released its updated information on weekend strikes against ISIS and said coalition forces had conducted 69 strikes consisting of 88 engagements, including nearly 30 strikes near Raqqa, Syria, that engaged seven ISIS tactical units and destroyed 20 fighting positions and a supply route.

Even though ISIS has lost significant amounts of territory in Iraq and Syria, experts said the terrorist group remains a global threat and probably will for years to come.