An armed man has been arrested inside the stadium where a memorial service will be held for Charlie Kirk.

Authorities are investigating why the individual, reportedly a former sheriff’s deputy carrying a knife and gun, made his way into the venue in Glendale, Arizona, before authorities had set up a security perimeter.

Tens of thousands of mourners, among them Donald Trump, the US president, are expected to descend on the arena on Sunday to remember Kirk, a conservative influencer who was shot dead last week on a college campus in Utah.

Organisers have told The Telegraph that security is being provided by the federal government and will be tighter “than the Super Bowl”.

Late on Friday, authorities arrested a man, who has not been named, said to have been behaving suspiciously inside Glendale’s State Farm Stadium just hours before Kirk’s memorial service was due to begin.

A federal source told Fox News that when agents approached him, he identified himself as a law enforcement official and presented out-of-date credentials, saying he was armed and at the venue to provide private security.

“This guy is a former deputy sheriff out of Idaho,” the source said. “They are going through his background and trying to figure out what he was up to there.”