GENEVA (Reuters) - The suspension of Nigeria’s most senior judge by President Muhammadu Buhari broke international human rights standards on independence of the judiciary and the separation of powers, a U.N. expert said on Monday.

Buhari, who was a military ruler in the 1980s and was voted into office in 2015, is hoping to win a new term in a presidential election scheduled to take place on Saturday.

The chief justice could preside over any 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.

“International human rights standards provide that judges may be dismissed only on serious grounds of misconduct or incompetence,” said Diego Garcia-Sayan, the U.N. special rapporteur on the independence of judges and lawyers.

“Any decision to suspend or remove a judge from office should be fair and should be taken by an independent authority such as a judicial council or a court,” he said in a statement.

Garcia-Sayan, who is mandated by the U.N. Human Rights Council to investigate legal and judicial independence, said dismissing judges without following legal procedures or offering a chance to contest the decision was incompatible with the independence of the judiciary.

Buhari suspended Chief Justice Walter Onnoghen on Jan. 25 following an order by a tribunal on public officials’ conduct and replaced him with Ibrahim Tanko Mohammad.

But four courts superior to the tribunal had already ordered a stay of proceedings and the tribunal had previously said it lacked jurisdiction over cases involving judicial officers, Garcia-Sayan said.

The U.N. statement said some of the judges and the defense lawyers involved in Onnoghen’s case had been subject to serious threats, pressures and interference.