A plea deal with five men accused of plotting the 9/11 attacks has been revoked after families of the victims complained about its leniency.

US Defence Secretary Lloyd Austin revoked the pre-trial agreement that had been reached the accused earlier in the week.

In a memo, Austin said he was revoking the authority of the officer overseeing the military court who signed the agreement.

Although the exact details of the original plea deal were not released, local reports suggested a guilty plea came in exchange for the prosecution agreeing not to seek the death penalty.

In the memo, Austin named five defendants, all of whom are held in the infamous Guantanamo Bay in Cuba - while the original deal named just three men.

The five men named in the memo were: Khalid Sheikh Mohammed, Walid Muhammad Salih Mubarak bin Attash, Mustafa Ahmed Adam al-Hawsawi, along with two others not mentioned in the original plea: Ramzi bin al-Shibh and Ali Abdul Aziz Ali.

They were accused of several charges, including attacking civilians, murder in violation of the laws of war, hijacking and terrorism.

Austin wrote to Brigadier General Susan Escallier: "I have determined that, in light of the significance of the decision to enter into pre-trial agreements with the accused... responsibility for such a decision should rest with me as the superior authority.

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"I hereby withdraw your authority. Effective immediately, in the exercise of my authority, I hereby withdraw from the pre-trial agreements."

Many family members of victims had criticised the terms of the deal struck as too lenient.

Brett Eagleson, the president of 9/11 Justice - which represents survivors and relatives of victims - had told the BBC earlier this week that the families were "deeply troubled by these plea deals".

Terry Strada, who lost her husband Tom and chairs the 9/11 Families United group, told the BBC she was "very pleased" to see the Pentagon revoke the plea deal and put the death penalty back on the table.

She said she would want to see the death penalty - if the men were found guilty - because it "fits the crime", not because she is "ghoulish or a horrible person".

She added: "They've murdered nearly 3,000 Americans on American soil... lives were just permanently altered on that day."

A lawyer at Guantanamo representing Khalid Sheikh Mohammed told The New York Times, that he was shocked by the sudden U-turn.

Gary Sowards said: “If the Secretary of Defence issued such an order, I am respectfully and profoundly disappointed that after all of these years the government still has not learned the lessons of this case. And the mischief that results from disregarding due process and fair play.”