US prosecutors will seek the death penalty against the suspected gunman in the Tree of Life synagogue massacre which left 11 worshipers dead.

Robert Bowers, 46, is accused of opening fire at the Pittsburgh synagogue during its Shabbat service in what is believed to be the worst antisemitic attack in US history.

The Justice Department said it will seek the death penalty on charges that include obstruction of free exercise of religious beliefs resulting in death, use and discharge of a firearm to commit murder, and possession of a firearm during a violent crime.

Prosecutors said: "Robert Bowers expressed hatred and contempt toward members of the Jewish faith and his animus toward members of the Jewish faith played a role in the killings." 

In October 2018 the shooter entered the Tree of Life Congregation synagogue in the city's Squirrel Hill neighbourhood, during a baby-naming service.

Prosecutors said they believe the death penalty is justified because Mr Bowers’s antisemitic views played a role in the shooting.

According to a federal notice prosecutors will argue that the shooting was intentional and he showed no remorse.

Mr Bowers faces 63 federal charges, including use of a firearm to commit murder, and hate crime charges.

A Justice Department news release in January said of the 63 charges that he faces, 22 carry the death penalty.