Isis has repeated its claim of responsibility for the Las Vegas attack while alleging that Stephen Paddock converted to Islam six months ago.

Investigators have not yet confirmed any link between the 64-year-old gunman and the terrorist group, with his girlfriend and relatives claiming he had no religious affiliation and was not an extremist.

In a new issue of its Arabic propaganda newspaper, Isis celebrated the worst mass shooting in modern American history with a graphic showing the Mandalay Bay hotel and casino stained blood red.

It boasted of the 58 people killed and 500 others injured, as well as of causing “panic and confusion among security services in America and a number of European countries”.

In an accompanying article, Isis recycled information on Paddock’s position and weapons from US news reports, claiming he was responding to calls for attacks on countries bombing its territories in Syria and Iraq.

Isis glossed over the fact Paddock shot himself – an action inconsistent with jihadi doctrine – and claimed he “rose as a martyr” while praising the man it calls Abu Abd al-Bar al-Amriki.

The kunya, a type of Arabic nickname, was first used in a claim of responsibility issued on Monday.

A graphic celebrating the Las Vegas attack and claiming Stephen Paddock converted to Islam six months ago, from Isis’ al-Naba propaganda magazine on 5 October

Used by Isis fighters and supporters to conceal their identity, the names are also published in propaganda statements celebrating terror attacks.

Analysts said Isis’ use of a kunya for Paddock either shows it was in communication with the gunman, or that it is mounting extensive efforts to bolster a false claim.

Raffaello Pantucci, director of International Security Studies at the Royal United Services Institute (RUSI), said the name would “ordinarily provide an indicator of some contact” as it should only be known by the terrorist and Isis contacts.

“But at the same time, it is also possible that the group would manipulate this, which would be a way of showing a link without it necessarily being real, and no one really being able to discount it,” he added.

Charlie Winter, a senior research fellow at the International Centre for the Study of Radicalisation and Political Violence (ICSR), said the “jury was out” on whether Isis was linked to the attack.

He told The Independent that claims issued through Isis’ Amaq news agency had been correct in the past but Las Vegas seems “extremely fishy”.

“There’s a hefty strategic logic behind every act of terrorism it claims – it’s not just communicating with us, the adversary, but with its supporters. It’s got to show them they’re not fighting for a lost cause,” Mr Winter added.

“It could be that Isis made a mistake, it could be that the sources and claiming methodology didn’t check out this time, and it could be an opportunistic claim.

“Perhaps Isis did a false claim this one time – it’s not definite but it’s one scenario.”

Las Vegas shooting – in pictures Show all 15 1 /15 Las Vegas shooting – in pictures Las Vegas shooting – in pictures People scramble for shelter at the Route 91 Harvest country music festival after gun fire was heard Getty Las Vegas shooting – in pictures People carry a person at the Route 91 Harvest country music festival after shots were fired David Becker/Getty Las Vegas shooting – in pictures People run from the Route 91 Harvest country music festival after gun fire was heard David Becker/Getty Las Vegas shooting – in pictures A handout photo released via Twitter by Eiki Hrafnsson (@EirikurH) showing concertgoers running away from the scene (C) after shots range out at the Route 91 Harvest festival on Las Vegas Boulevard EPA/Eiki Hrafnsson Las Vegas shooting – in pictures People lie on the ground at the Route 91 Harvest country music festival after hearing gun fire Getty Las Vegas shooting – in pictures A man in a wheelchair is taken away from the Route 91 Harvest country music festival after hearing gun fire David Becker/Getty Las Vegas shooting – in pictures People stand on the street outside the Mandalay Bay hotel near the scene of the Route 91 Harvest festival on Las Vegas Boulevard EPA/Paul Buck Las Vegas shooting – in pictures FBI agents confer in front of the Tropicana hotel-casino after a mass shooting during a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Las Vegas police run by a banner on the fence at the Route 91 Harvest country music festival grounds after shots were fired David Becker/Getty Las Vegas shooting – in pictures An injured person is tended to in the intersection of Tropicana Ave. and Las Vegas Boulevard after a mass shooting at a country music festival Ethan Miller/Getty Las Vegas shooting – in pictures Metro Police officers pass by the front of the Tropicana hotel-casino after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures A woman sits on a curb at the scene of a shooting outside of a music festival along the Las Vegas Strip AP/John Locher Las Vegas shooting – in pictures A cowboy hat lays in the street after shots were fired near a country music festival in Las Vegas Getty Las Vegas shooting – in pictures Las Vegas Metro Police and medical workers stage in the intersection of Tropicana Avenue and Las Vegas Boulevard South after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Sheriff Joe Lombardo (2-R) speaking during a press briefing in the aftermath of the active shooter incident on Las Vegas Boulevard EPA

Mr Winter said that if investigations show Isis’ claim is false, the damage to its reputation among supporters would be limited as they trust the group’s propaganda over Western authorities.

“The victory has already been planted internally and no amount of evidence to the contrary will convince people fighting for or believing in the group that it’s wrong,” he added.

“We’ll know one way or another in the next few weeks but Isis’ efforts to associate itself with an attack like this show it isn’t in a particularly good state at the moment.”

The terrorist group has been intensifying calls for global terror attacks while suffering heavy losses in its dwindling “caliphate” in Iraq and Syria, with the latest message purporting to come from leader Abu Bakr al-Baghdadi.

In a 46-minute audio recording released last week, he urged jihadis to “intensify one attack after another against the infidels”, with the message followed by Isis-related attacks in Marseille and Edmonton.

Isis has released detailed guidance on launching terror attacks, including on how to obtain guns in the US and naming concerts as a prime target.

The FBI said its investigation had not yet found any link to the group but local police suggested Paddock may have been radicalised amid continuing confusion over his potential motives.

“Did this person get radicalised unbeknownst to us?” Sheriff Joseph Lombardo asked. “We want to identify that source.

Guns are scattered around the hotel suite where Paddock holed up for four days (ABC News)

“The fact that he had the type of weaponry and amount of weaponry in that room, it was preplanned extensively and I’m pretty sure he evaluated everything that he did and his actions, which is troublesome.”

Paddock booked rooms next to other music festivals in the months before Sunday’s attack, including overlooking the Lollapalooza festival in Chicago in August and the Life Is Beautiful show near the Vegas Strip in late September.

Authorities are looking into the possibility Paddock planned additional attacks, including a car bombing, having found 1,600 rounds of ammunition in his car, along with fertiliser that can be used to make explosives and 50lbs of Tannerite, a substance used in explosive rifle targets.

Paddock had an arsenal of 23 weapons in his hotel room – a dozen included “bump stocks” attachments that speed up the rate of fire – and another 19 at home.

His girlfriend, Marilou Danley, told FBI agents on Wednesday she had not noticed any changes in his mental state or indications he could become violent after being sent on a trip to her native Philippines before the attack.

Paddock’s brother, Eric, claimed he had “no religious affiliation, no political affiliation” or history of mental illness.

The profile of Paddock developed so far is of a high-stakes gambler and “disturbed and dangerous” man who acquired an arsenal over decades, Sheriff Lombardo said, while admitting that much of his “secret life” may never be understood.