The National Rifle Association has suspended its top lobbyist after accusing him of complicity in a failed coup against the gun group’s chief executive Wayne LaPierre.

Chris Cox, the NRA’s second-in-command, allegedly worked with public relations firm Ackerman McQueen, former NRA president Oliver North and NRA board member Dan Boren to try to force out Mr LaPierre.

The accusation came in a lawsuit filed on Wednesday night in New York state Supreme Court against Mr North who led the coup attempt shortly before the group’s annual convention in April.

In the lawsuit, the NRA said that text messages and emails demonstrated that “another errant NRA fiduciary, Chris Cox – once thought by some to be a likely successor for LaPierre – participated” in what was described as a conspiracy.

The court filing includes text exchanges in which Mr Cox and a board member appear to be discussing an effort to oust Mr LaPierre, although the full context is unclear. The NRA is conducting an internal review of the matter.

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Andrew Arulanandam, a spokesperson for the organisation, said that Mr Cox had “been placed on administrative leave” on Thursday.

Mr Cox said in a statement: “The allegations against me are offensive and patently false. For over 24 years I have been a loyal and effective leader in this organisation.

"My efforts have always been focused on serving the members of the National Rifle Association, and I will continue to focus all of my energy on carrying out our core mission of defending the Second Amendment.”

The suit – the latest in a series of legal actions stemming from the gun group’s internal turmoil – is likely to send new shock waves through the NRA.

While Mr North served as president for just one year, Mr Cox has worked for the NRA since 1995 and has led its lobbying arm since 2002. He has been a leading presence at the organisation's gatherings.

Among other things, he has been a fervent defender of the AR-15, the semi-automatic rifle used in many mass shootings, telling attendees at the group’s convention last year that “we have an AR culture that’s on display all over the exhibit halls this weekend”.

Together, Mr Cox, 49, and Mr LaPierre, 69, have been the public faces of the NRA, the twin architects of its strategy. But they have had an uneasy relationship, and their staff are somewhat siloed from each other.

Mr Cox runs the NRA’s lobbying arm, the Institute for Legislative Action, which has a separate media relations team from the NRA’s, and his choice of consultants has also sometimes diverged from Mr LaPierre’s.

As Mr North’s coup attempt played out at the convention this spring, some people inside the NRA said Mr Cox largely kept quiet and appeared to be hedging his bets.

Jennifer Baker, a spokeswoman for the NRA’s lobbying arm, said Mr Cox and Mr LaPierre had “worked closely together for a quarter of a century, and any notion that Chris participated in a coup is absurd".

"Chris Cox is known as a calming force who always acts in the best interests of our members by effectively defending the Second Amendment, so it’s not surprising that board members would reach out to him for advice during tumultuous times.”

But Carolyn D Meadows, who succeeded Mr North as NRA president, said in a statement: “I fully support the actions undertaken today.

"The NRA is moving forward on all fronts, especially with regard to serving our members and focusing on the crucial upcoming elections.”

The genesis of the dispute between the NRA and Mr North is a related legal battle between the NRA and its most prominent contractor, the Oklahoma-based advertising firm Ackerman McQueen, which employed Mr North.

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The NRA has sued Ackerman, claiming it withheld documents and records from the gun group, and some officials have suggested the company may also have been overcharging the gun group. Ackerman, which has said it did nothing improper, filed a counter suit claiming that it was smeared by the NRA.

In yet another lawsuit, the NRA has accused Ackerman of breaching confidentiality clauses in its contract and smearing Mr LaPierre.

The new lawsuit seeks to block Mr North’s attempt to have the NRA pay his legal fees, which he has sought as he fields requests to cooperate with other litigation as well as a Senate inquiry.