An online auction for the gun that George Zimmerman used to kill Trayvon Martin saw bids rise to $65m early on Friday.

The top bidder used the screen name “Racist McShootface”, though it was unclear if the offer was serious. The account was later deleted.

The United Gun Group website hosted the auction after cancelled the sale amid widespread criticism. Bids started at $5,000.

The Florida neighbourhood watch volunteer’s 2012 fatal shooting of the unarmed black teenager and subsequent acquittal sparked a national debate on race relations.

GEORGE ZIMMERMAN Seminole County Sheriff's Office booking photo

George Zimmerman was acquitted over the teenager’s death in July 2013

United Gun Group said on Thursday night it had withdrawn 32-year-old Mr Zimmerman’s listing.

“Our mission is to esteem the 2nd amendment and provide a safe and secure platform for firearms enthusiasts and law-abiding citizens,” the organisation said in a statement.

“Our association with Mr Zimmerman does not help us achieve that objective.”

But the 9mm Kel-Tec PF-9 pistol was back up on United Gun Group’s website early on Friday.

Mr Zimmerman told the Orlando Sentinel that, which hosted the original listing, was not “prepared for the traffic and publicity surrounding the auction of my firearm”.

But GunBroker said in a statement: “We want no part in the listing on our web site or in any of the publicity it is receiving.”

Mr Zimmerman told Orlando TV station WOFL the gun had been returned to him by the US Justice Department following his 2013 acquittal in the 17-year-old’s death.

Zimmerman described the weapon as “an American Firearm Icon”.

He said he would use proceeds from the sale to fight “Black Lives Matter” violence against law enforcement officers and to counter “Hillary Clinton’s anti-firearm rhetoric”.

The money was also to go towards ending the career of Angela Corey, who led the prosecution against Mr Zimmerman, he said.

The listing ended with “if you want peace, prepare for war” in Latin.

Mr Zimmerman claimed he has been subjected to death threats since the shooting.

He added: “I’m a free American. I can do what I want with my possessions.”

A lawyer for Trayvon Martin’s family said the foundation in his name was focused on ending senseless gun violence in the US and had no comment on the auction.