KENOSHA, WISCONSIN (REUTERS) - Teenager Kyle Rittenhouse told jurors in his Wisconsin murder trial on Wednesday (Nov 10) that "I did what I had to do" after enduring threats and attacks while carrying an AR-15-style rifle during chaotic racial justice protests, breaking down in tears on the witness stand.

In dramatic and risky testimony in his own defence, Rittenhouse tried to portray himself as wanting to help others during the protests last year in the city of Kenosha and opened fire only in self-defence after being attacked and ambushed.

Prosecutors have described Rittenhouse as a vigilante who killed two protesters.

Questioned by the prosecution, Rittenhouse said, "I did what I had to do to stop the person who was attacking me."

"By killing them?" Kenosha County Assistant District Attorney Thomas Binger asked.

"Two of them passed away but I stopped the threat from attacking me," Rittenhouse replied.

"By using deadly force?" Binger asked.

"I used deadly force," Rittenhouse said. "...I didn't know if it was going to kill them. But I used deadly force to stop the threat that was attacking me."

Rittenhouse, 18, is charged in the killing of Joseph Rosenbaum, 36, and Anthony Huber, 26, and the wounding of Gaige Grosskreutz, 27, during racial justice protests on Aug 25, 2020. He has pleaded not guilty and has said he acted in self defence.

By the night of the shootings, Kenosha had endured two nights of chaotic protests over the police shooting of a local Black man, Jacob Blake. Several businesses were burned to the ground and there were incidents of looting. Police used rubber bullets and tear gas to control the crowds.

Dressed in a navy blue suit and dark blue tie, Rittenhouse was composed on the witness stand until his attorney began asking him to detail his encounter with Rosenbaum, who video evidence showed was pursuing the teen when he turned and shot him four times.

"I didn't notice Mr Rosenbaum until he came out from behind the car and ambushed me," Rittenhouse told the jury, before he started to breathe heavily and lose his composure, shedding tears as the judge called for a break.

Moments earlier, Rittenhouse testified that Rosenbaum threatened twice to kill him before their final encounter, telling a group he was with "I'm going to cut your fucking hearts out." He was 17 at the time of the shootings.

Rittenhouse testified that he was asked to help guard a used car dealership along with other armed men, including one who was a boyfriend of his sister at the time. Rittenhouse said his objective that night was to provide medical aid to anyone hurt.

In addition to five felonies, he has been charged with underage possession of his weapon, a powerful semi-automatic rifle.

Before the Rosenbaum shooting, Rittenhouse said he was walking down the street and heard "somebody scream 'burn in hell' and I replied with 'friendly, friendly, friendly' to let them know, 'Hey, I'm just here to help... I don't want any problems. I just want to put out the fires if there are any.'"

Prosecutors during the trial have emphasised that Rittenhouse was the only person to have shot anyone on a night when hundreds of protesters had taken to the streets, some peacefully and others engaged in arson, looting and rioting.

The Kenosha unrest erupted after a white policeman shot and seriously wounded Jacob Blake, a Black man. That shooting took place against the backdrop of nationwide protests over racism and police brutality following the May 2020 murder of George Floyd, another Black man, by a policeman in Minneapolis.

The prosecution rested its case on Tuesday.

The case is the most high-profile civilian US self-defence trial since George Zimmerman was acquitted in the fatal shooting of Trayvon Martin, an unarmed Black teenager, in Florida in 2013.

Like Zimmerman, Rittenhouse has emerged as a divisive figure and politics has coursed through the case. He is a hero to some conservatives who believe in unfettered gun rights and see the shootings as justified during the chaos in Kenosha, while many on the left see him as a symbol of a gun culture run amok.

During five days of testimony, prosecutors have tried to paint Rittenhouse as a vigilante killer who used deadly force without justification.

Binger pressed Rittenhouse on his playing of video games like "Call of Duty," asking whether one of the main objective of such games is to shoot a lot of people.

"It's just a video game. It's not real life," Rittenhouse replied.