ABUJA (Reuters) - Nigeria’s President Muhammadu Buhari suspended the country’s most senior judge on Friday weeks ahead of a presidential election, in what his challenger called an act of dictatorship and the bar association called an “attempted coup”.

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Buhari, who was a military ruler in the 1980s and was voted into office in 2015, is seeking a fresh term in an election scheduled to take place on Feb. 16.

The chief justice could preside over a dispute over the election result. Nigeria’s judiciary has helped resolve electoral disputes in past votes, some of which have been marred by violence and vote rigging.

Chief Justice Walter Onnoghen has been asked to appear before a tribunal over allegations of breaching asset-declaration rules. He has not responded to the charges and his lawyers say the tribunal does not have the authority to try him.

Under Nigerian law, state officials must declare their assets before taking office and after they leave.

“With the directive of the CCT (Code of Conduct Tribunal) in a letter dated 23rd January, 2019, accordingly, I hereby suspend Hon Justice Walter Nkanu Samuel Onnoghen as the Chief Justice of Nigeria until the final determination of the case against him,” Buhari said.

In a later tweet, the president said security agencies had traced “suspicious transactions running into millions of dollars to the CJN’s personal accounts, all undeclared or improperly declared as required by law”. He gave no further details. CJN refers to the chief justice of Nigeria.

A media aide to Onnoghen did not respond to phone calls and text messages seeking comment.

Tanko Mohammed, a judge from the northeastern state of Bauchi, was named as the chief justice’s acting replacement.

On Thursday, an appeals court had issued an interim order to halt charges being brought against the chief justice.

Buhari’s main challenger in the presidential vote, former vice president Atiku Abubakar, candidate for the main opposition People’s Democratic Party, issued a statement titled: “The purported suspension of CJN Onnoghen is an act of dictatorship taken too far.”

“(I) call on Justice Onnoghen and the judiciary to resist with every legal and constitutional means that they can muster,” he said. “This act of desperation is geared towards affecting the outcome of the 2019 Presidential elections,” said Atiku.

The Nigerian Bar Association, in a statement, said it “unequivocally rejects and condemns this attempted coup against the Nigerian judiciary and evident suspension of the Nigerian constitution”.

“The action of the executive portends a slide into anarchy and complete deconstruction of the Rule of Law and due process,” it said in the statement.

It urged a reversal of the suspension and called on parliament to assert its “constitutional authority” to intervene.