Video footage showing Sandra Bland in jail has been released by authorities in Texas in a bid to dispel rumours she was already dead before arriving there.

Ms Bland, an African-American, was found hanged in her cell at Waller County Jail three days after she was arrested by a white police officer following a minor traffic offence.

The 28-year-old's death has raised a number of questions after it gained international attention amid increased scrutiny on police treatment of minorities.

A number of rumours have circulated online, including the suggestion that Ms Bland had already died before she arrived at the jail.

Judge Trey Duhon said such theories had prompted death threats against county officials, while hacker group Anonymous has also reportedly attempted to take down county websites.

"Because of some of the things that's gone out on social media, this county has been literally attacked," Mr Duhon said at a news conference, adding that the FBI would be investigating the most serious threats.

Mr Duhon said Ms Bland was "alive and well" until she was found in her jail cell on 13 July.

Authorities have ruled her death was a suicide, but the woman's friends and relatives say they do not believe the official version of events.

In the footage released by authorities, Ms Bland can be seen being taken out of a patrol car at the jail before being questioned by an official, the Associated Press has reported.

She is then reportedly briefly placed in a holding cell before her mugshot is taken and she makes a phone call.

Mr Duhon said: "This is Sandra Bland. There's no other way around it. This video has not been altered or doctored in any way. These are the raw files."

Ms Bland, formerly of Chicago, was pulled over on 10 July for failing to signal when changing lanes.

The incident escalated into an altercation between Ms Bland and officer Brian Encinia, 30, when she apparently questioned an order to put out her cigarette and leave her car.

In footage released by police, the officer can be seen aiming a Taser at her and threatening to "light her up".

She was then taken into custody charged with assaulting an officer.

The case is being investigated by the Texas Rangers and the FBI.