A newly elected US congressman has apologised after allegedly assaulting a news reporter one day before the special election. Greg Gianforte (R-Mont.) was addressing the incident for the first time as part of his victory speech

"Last night, I made a mistake and I took an action that I cant take back – and I'm not proud of what happened," Gianforte said during his victory rally in Bozeman, Montana shortly before 11pm local time.

"I should not have responded in the way that I did and for that I'm sorry. I should not have treated that reporter that way and for that, I am sorry Mr. Ben Jacobs," he said to the reporter from The Guardian.

His campaign initially claimed that the reporter "aggressively shoved a recorder in Greg's face," grabbing the candidate's wrist and pushing him to the ground.

But a Fox News reporter who witnessed the altercation said that Gianforte "grabbed Jacobs by the neck with both hands and slammed him to the ground," adding that Jacobs did not "show any form of physical aggression toward Gianforte" before he grabbed the reporter's neck.

Gianforte secured 51% of the vote while his Democratic rival Rob Quist took 43%.

Gianforte is scheduled to appear in county court sometime before 7 June – the charge carries a maximum fine of $500 or a prison term of no more than six months.

The last-minute chaos cast even more of a spotlight on the race, one of the few special elections of 2017.