The group did not name Stephen Paddock, the man identified by police as the shooter, in a statement released via its Amaq propaganda agency.
“The Las Vegas attacker is a soldier of the Islamic State and carried out the operation in response to appeals targeting coalition countries,” it said.
“The Las Vegas attacker converted to Islam several months ago.”
The claim was prefaced with the phrase “a security source to Amaq Agency” – a phrase frequently used after attacks that were not directed by Isis.
Its latest claim could not immediately be verified and Paddock’s supposed conversion to Islam has not been confirmed.
Paddock’s apparent suicide also conflicts with jihadi ideals of “martyrdom”, which normally sees Isis-inspired attackers kill themselves in suicide bombings or by forcing security forces to shoot them dead.
Police said the 64-year-old white American opened fire from the 32nd floor of a nearby hotel, where he had multiple weapons and is believed to have killed himself.
More than 50 people have been confirmed dead and 200 injured in the shooting, making it the deadliest in US history.
The shooting started shortly after 10pm local time, with footage showing concert-goers throwing themselves to the ground and running as several extended rounds of automatic gunfire rang out.
Police initially said the shooting was not being treated as a terror attack but no updated statement has been made since Isis released its claim.
It came days after Isis released a speech purporting to be from the group's leader.
A 46-minute audio recording appeared to show Abu Bakr al-Baghdadi praise the jihadis killed in the battle to retake Mosul and other former Isis territories.
He urged followers to “intensify one attack after another against the infidels”, following a spike in global terror attacks.
Security officials and experts have long warned that Isis will seek to maintain momentum and legitimacy through terror as its so-called “caliphate” dwindles in Iraq and Syria.
It came after the group claimed responsibility for a stabbing attack that left two young women dead in the French city of Marseille earlier on Sunday.
Isis was also linked to a car and knife attack in Edmonton, Canada, where a police officer found a flag used by the group in the perpetrator's car.
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