Opposition MPs Thursday demanded sweeping constitutional reforms to a full parliamentary system in Kuwait a day after the top court scrapped legislative polls and reinstated the previous house.

"We affirm that constitutional reforms to achieve a full parliamentary system... have become a necessity" to resolve the lingering political crisis, said a statement signed by 35 opposition MPs of the 50-member parliament.

Opposition groups have been pressing for a full parliamentary system with an elected government to break the ruling Al-Sabah family's monopoly in key posts, in addition to legalising political parties.

The statement, issued after a lengthy meeting, strongly criticised the court ruling and warned against "involving the judiciary in political disputes."

On Wednesday the constitutional court, whose rulings are final, declared February's legislative election won by the opposition illegal and reinstated the previous pro-government parliament.

It based its decision on the grounds that two decrees dissolving the previous parliament and calling for a fresh election were illegal.

Opposition MP Faisal al-Muslim described the ruling as "a political verdict that has plunged the country into a tunnel," and called on the government to dissolve the reinstated parliament and call for fresh elections.

About 30 MPs from the previous parliament, mostly opposition members, have said they will not join the reinstated house and submitted their resignations.

Housing Minister Shuaib al-Muwaizri, the only elected MP in the cabinet, on Thursday submitted his resignation in protest about the developments.

The opposition Islamist Ommah Party, which is not recognised in Kuwait, called in a statement for a new constitution accepting the rotation of power and an elected government.

The Progressive Movement called for "political and constitutional reforms to transform Kuwait into a full parliamentary system" and urged the Al-Sabah family to end its monopoly on the premiership and key ministries.

The Umbrella for Kuwait Action, a civil society group, called for Kuwait to become a constitutional monarchy as the only way to overcome the ongoing political crisis.