A woman who rushed to her husband's help in the aftermath of the Boston marathon blasts had no idea that the homemade bombs had set her back on fire.

Jessica Kensky, a nurse, said that in the moments after the 2013 blasts, she went to help her husband whose leg had been torn off by shrapnel. Working on instinct and training, she was applying a tourniquet when she noticed that someone was talking to her.

"There was smoke, there was blood. I was most focused on my husband, he was right next to me still, and his foot and his leg were kind of detached" she said. "A man came over as I was trying to fumble to put a tourniquet on Patrick and said, "Ma'am you're on fire, you're on fire"."

Ms Kensky was giving testimony on Monday at the trial of Dzhokhar Tsarnaev in Boston, the Associated Press reported. Mr Tsarnaev, 21, is accused of killing three people and injuring 264, including the Ms Kensky and her husband, in the blasts that were set off at the finish line of the race on April 15 2013.

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Ms Kensky, who rolled into the courtroom in a wheelchair, lost her left leg on the day of the bombing. Her right leg was amputated in January of this year because it had failed to heal from injuries sustained in the blast.

Her husband, Patrick Downes, also lost a leg in the blast. The couple were taken to separate hospitals in the aftermath of the attack and did not see each for two weeks, the AP said. They completed the race the following year in wheelchairs.

Last week, Mr Tsarnaev's lawyers said the defendant and his older brother were jointly responsible for the attack as well as the fatal shooting of a police officer three days later.

They said that Mr Tsarnaev's elder brother, Tamerlan Tsarnaev, 26, who died following a gun-battle with police three days after the bombing, was the driving force behind the attack. Mr Tsarnaev has pleaded not guilty to the multiple charges he faces.

Prosecutors have told the court that Dzhokhar Tsarnaev also read jihadist magazines online and "believed that he was a soldier in a holy war against Americans".