Geneva - 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.