NAIROBI - Kenya's High Court ruled Thursday that a drive by President Uhuru Kenyatta to change the constitution was illegal, stopping what his critics have called a political move designed to check his deputy, whom he has fallen out with publicly.

Parliament has already passed the proposed amendments, popularly known as the Building Bridges Initiative, which mark the biggest change to the East African nation's government structure since a new constitution was adopted in 2010.

But issuing a ruling on several challenges lodged by various parties, a five-judge bench of the court said Kenyatta had used a constitutional provision reserved for citizens to initiate the changes, making the process illegal.

"The president cannot be both player and umpire in the same match," said Jairus Ngaah, one of the judges.

The government, which wants to hold a referendum after Kenyatta signs the bill into law, said it will appeal the ruling.

Kenyatta says the bill promotes the sharing of power among competing ethnic groups to reduce cyclical election violence and is not targeting anyone.

It will create 70 new constituencies, return the role of Cabinet ministers to elected members of Parliament and create several powerful new posts: a prime minister, two deputies and an official leader of the parliamentary opposition.

Kenyatta initiated the changes with the backing of former Prime Minister Raila Odinga, after the two made peace in January 2018 following a divisive presidential election the previous year in which the president beat Odinga.

The rapprochement isolated Kenyatta's deputy, William Ruto, who wants to succeed his boss when he steps down next year after serving the constitutionally allowed two, five-year terms.

The constitutional amendments are partly designed to tame Ruto's political ambitions by making it possible to cobble together an alliance against him, said John Githongo, a prominent anti-graft campaigner.

"It is very clear that some of these alignments are to sideline him," he said.

Ruto's allies have loudly opposed the constitutional changes bill in Parliament and outside.

"I don't think we have a constitutional problem in Kenya. ... The biggest problem in Kenya is an economic problem," Ndindi Nyoro, a pro-Ruto lawmaker, said on local Citizen TV.