An Egyptian court yesterday ordered the dissolution of the Freedom and Justice Party (FJP), the political wing of the already banned Muslim Brotherhood movement.
The decision comes after the authorities designated the Brotherhood a "terrorist organisation" in December following the ouster of Islamist president Mohamed Morsi by the military.
The FJP had come out on top in every election in Egypt between its creation in the wake of the country's Arab Spring uprising in 2011 and Morsi's removal in July 2013.
In its ruling, the Supreme Administrative Court ordered "the dissolution of the Freedom and Justice Party because it broke the law regarding political parties".
According to media reports, the decision is final and not open to appeal.
The military toppled Morsi, Egypt's first democratically elected president, after massive protests calling for his removal following a single year of turbulent rule.
Since then, a crackdown by the military-installed authorities on his supporters has killed 1,400 people in street clashes, and some 16,000 Islamists and protesters have been jailed.
At least 200 people have also been sentenced to death in speedy mass trials, including Brotherhood leader Mohamed Badie, although none of the sentences has been carried out so far.
Morsi himself is on trial on various charges, and the army chief who overthrew him, Abdel Fattah al-Sisi, replaced him after winning a presidential election in May.