The longtime chief executive of the National Rifle Association, Wayne LaPierre, is stepping down at the end of the month, the gun rights organization has announced.

The NRA issued a short statement from LaPierre via X, formerly known as Twitter, in which he said: “I’ve been a card-carrying member of this organization for most of my adult life, and I will never stop supporting the NRA and its fight to defend second amendment freedom. My passion for our cause burns as deeply as ever.”

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Membership of the association had dropped off significantly in recent years, as mass shootings rose across the US and legal action was taken against the NRA over allegations of corruption, amid financial struggles.

LaPierre, 74, said his departure would be effective from 31 January. He has been in charge of the NRA since 1991. The organization said Andrew Arulanandam, the head of NRA’s general operations, will become the interim chief executive and vice-president.

While LaPierre cites ill health for standing down, the timing comes just days before the start of a civil trial in New York that is poised to scrutinize his leadership.

A lawsuit from the New York attorney general Letitia James accuses LaPierre and other executives of illegally diverting tens of millions of dollars from the NRA and spending organization funds on personal trips, “no-show” contracts and other questionable expenditures.

The trial starts in Manhattan on Monday and LaPierre is expected to be among the witnesses.

James is seeking to ban LaPierre and the other executives from serving in the leadership of any not-for-profit or charitable organization conducting business in New York, which would effectively remove them from any involvement with the NRA.

The Guardian reported in 2020 how cracks in the NRA began to emerge as members and powerful donors shared concerns about its spending, management and the widening gap between leadership and the rank and file.

James aired the concerns in a 168-page lawsuit that outlined the workings of an organization in which, allegedly, dissent was not tolerated, spending was not disclosed or approved through the proper channels and oversight was negligent.

“Brazen illegaility” in the NRA was rife, she said.

Reuters and the Associated Press contributed reporting