An official of the now-banned Muslim Brotherhood said the group has been subject to an across-the-board restructuring in its leadership, as the movement announced the establishment of a new bureau operating overseas.

In his first TV interview on Al Jazeera station on Wednesday, Ahmed Abdel Rahman, head of the Brotherhood's newly-established office, said almost 60-70% of the Islamist movement's leadership has been reshuffled, with youths assuming many of the major roles.

The official said the new bureau, whose creation was announced a few days ago, would take care of hundreds of the group's members who fled the security crackdown at home, and press ahead with the local bureau's fight against the Egyptian authorities that the movement accuses of mounting a coup against a democratically elected government.

The bureau, whose location was not disclosed, comprises of 11 members selected following elections in Egypt and abroad, including former ministers under the Brotherhood's deposed president Mohamed Morsi, Amr Darag and Yahia Hamed, Abdel Rahman said.

Asked about the Brotherhood's political blunders, the official said "we were mistaken when we thought that a revolutionary course would restore stability to the country," in reference to protests that followed Morsi's July 2013 ouster which led to the death of hundreds of Islamists. Most of those were killed in August 2013 when police forces forcibly dispersed a sizeable protest vigil in Cairo.

Abdel Rahman has been a senior member of the Brotherhood for years, and was an MP under Morsi.

Elected in June 2012 after the overthrow of long-time autocrat Hosni Mubarak, Morsi was ousted a year later after a rule marred by deep divisions in Egyptian society, unrest and a faltering economy.

The 86-year-old Brotherhood is currently facing one of its most serious existential challenges, with a relentless security crackdown that has jailed thousands of its members and supporters.

On Tuesday, Morsi was sentenced to 20 years in prison over charges of ordering the arrest and torture of demonstrators involved in clashes in 2012 when he was still Egypt's elected president. It was the first verdict against the former leader.

Earlier in April, the spiritual leader of the group, Mohamed Badei, was sentenced to death over violence related charges. The ruling is subject to appeal.

Authorities say the Muslim Brotherhoods is a terrorist organisation, but the group insists it is committed to peaceful activism.