Kuwait's constitutional court on Wednesday declared February's legislative polls in which the opposition swept to victory illegal and reinstated the previous pro-government parliament, state media said.
Leading opposition MP Mussallam al-Barrak described the verdict as "a coup against the constitution" and called for the opposition to take a united stand.
"The court declared that the emiri decree that called for the 2012 election was unconstitutional and ordered reinstating the previous assembly," the state-run KUNA news agency reported.
Rulings by the Gulf state's highest court are final and cannot be challenged.
Kuwait Emir Sheikh Sabah al-Ahmad Al-Sabah issued a decree in early December dissolving the parliament following youth-led street protests calling for reforms and for the sacking of former prime minister Sheikh Nasser Mohammad al-Ahmad al-Sabah.
A few days later, the emir issued another decree inviting Kuwaitis to elect a new parliament on February 2.
The court ruled that the second decree was "unconstitutional", thus nullifying the results of the general elections in which the opposition scored an impressive victory.
The previous parliament was controlled by a pro-government majority.