The death sentences were carried out despite calls by international human rights organisation to halt the executions.
Egyptian authorities on Wednesday executed nine youths convicted of assassinating the country's prosecutor-general in 2015, according to local media and judicial sources. It brought to 15 the number of executions in Egypt this year.
Hisham Barakat was killed in June 2015 when a car bomb struck his convoy in Cairo. The nine men hanged were among 28 people sentenced to death in 2017 for involvement in his murder.
The son of senior Muslim Brotherhood leader Mohamed Taha Wahdan was among those condemned to death.
The death sentence was carried out despite calls by international human rights organization – including Amnesty International – for the Egyptian authorities to halt the execution.
"There is no doubt that those involved in deadly attacks must be prosecuted and held accountable for their actions but executing prisoners or convicting people based on confessions extracted through torture is not justice," said Amnesty's North Africa campaigns director, Najia Bounaim.
"At least six men have already been executed earlier this month after unfair trials. Instead of stepping up executions the Egyptian authorities should take steps to abolish the death penalty once and for all," Bounaim said.
Barakat was the highest Egyptian official to have been killed in a militant attack since 2013.
Egyptian authorities have yet to confirm the executions.
In February, Egyptian authorities executed six people in two different cases for killing the son of a judge and a senior police officer.
Egypt was roiled by turmoil when the military deposed Mohamed Morsi, the country's first democratically elected president, in a 2013 coup.
Muslim Brotherhood targeted
No one claimed the 2015 attack against Barakat but authorities pointed the finger at members of the Muslim Brotherhood of ex-president Morsi, who was ousted in a coup by President Abdel Fattah al Sisi.
Since Sisi came to power, hundreds of Morsi supporters have been sentenced to death, while the former president and top Brotherhood figures have also faced trial.
Egypt's current government outlawed the Muslim Brotherhood just months after Sisi deposed Morsi and branded it a terrorist organisation.
Many of the death sentences have been handed down at mass trials involving hundreds of defendants and lasting just days.