For a long time, the "Islamic State of Iraq and Syria" (ISIS) was known to claim responsibility only for terror attacks it had planned or inspired, but its credibility in this regard has considerably decreased in recent months, in conjunction with its successive military defeats, officials and experts said.

On Sunday (October 1st), the group claimed responsibility for the Las Vegas attack in the US, saying that the shooter, a 64-year-old retired accountant, was a "soldier" of the group.

The next day, the group put out a second statement claiming serial gambler Stephen Paddock had recently converted to Islam and was known by the nom de guerre Abu Abdel Bar al-Amriki.

Investigators and ISIS experts have widely questioned this claim and said they have found "no connection" between Paddock and any international terrorist group.

"Today ISIS tends to claim every attack because it is going through a military regression" and needs to "maintain a presence in the media space", French Interior Minister Gerard Collomb said Tuesday.

The group has always used the same method to claim responsibility for an attack, even if it failed or was thwarted.

ISIS requires attackers to indicate their allegiance to the group either before, or during the attack.

If that was not possible, the perpetrator had to leave proof of that in his home or car, even if it was just the group's black banner, or a video or audio recording indicating his allegiance.

But doubts over the group's claims of responsibility first started to surface after the July 2016 Nice attack, in which 86 people were killed when a 31-year-old Tunisian drove his truck into a crowd.

Even though ISIS rushed to claim responsibility for the attack, no evidence was found that tied the driver, Mohammed Lahouaiej Bouhlel, to ISIS or extremist ideology.

Dubious claims

"This massacre had nothing to do with jihadism, the perpetrator had huge psychological problems," Farhad Khosrokhavar, an expert on Islam from the School for Advanced Studies in the Social Sciences in Paris (EHESS), told AFP.

"But no one listens. There are moments when societies are blind and they then fall into the Islamic State's trap," he said.

Dubious claims of responsibility have been mounting as the extremist group suffers successive defeats in Syria and Iraq, and his "caliphate" shrinks.

"ISIS in recent months has made a number of demonstrably false claims for attacks and incidents that had no jihadi terror nexus," Paul Cruickshank from the Combating Terrorism Centre at West Point said.

"ISIS, desperate for attention, will claim just about anything these days knowing their supporters will not believe the government or media," he said.

If the Las Vegas shooter "is a convert and made contact with ISIS, someone would have to know", Islamic extremism expert Shiraz Maher wrote on Twitter.

"Friends, family, law enforcement will shed light on that," added the researcher and author from King's College London university.

"The group's defeats in the field and the loss of its major strongholds, such as Mosul in Iraq and al-Raqa in Syria, explain its latest improvisation in claims of responsibility," said Islamic movements expert Mathieu Guidère.

"Today, the official in charge of the group's Amaq propaganda agency sits in front of the television [watching the news] ... and issues claims of responsibility," he said.

"We are no longer facing individuals who demand proof," he said. The Amaq official "claims responsibility for nearly everything that passes under his eyes".