President Muhammadu Buhari Picture: Reuters/Darren Ornitz/File Photo

Abuja - Nigeria's government has denied suggestions that the suspension of the country's top judge on corruption charges was linked to next month's election.

President Muhammadu Buhari replaced Chief Justice Walter Onnoghen on Friday, sparking claims he had breached the constitution and was trying to manipulate the judiciary.

The European Union, Britain and the United States each issued statements at the weekend expressing concern at the development, as elections are due on February 16.

But Buhari's spokesman said Sunday that there was no connection.

"In Nigerian law there is no such linkage," Garba Shehu said in a statement.

"The CJN (Chief Justice of Nigeria) does not run the election. Nor is he the first arbiter of any electoral complaints.

"He and the Supreme Court will only get involved as the final arbiter at the end of the appellate process...

"To link the CJN to the elections in this way is illogical unless they assume that election complaints will be filed and go all the way to the Supreme Court."

Shehu's statement was his second against the EU, Britain and the United States, which are all scheduled to have election monitors on the ground.

His later comments were more conciliatory in tone than the first, in which the government rejected outside "interference" and said the issue was an internal matter.

Onnoghen is accused of failing to declare foreign currency bank accounts, in breach of rules governing the declaration of assets by public officials.

Shehu maintained that Onnoghen's position was "untenable" given the case against him and the president was forced to act because the judge had not stepped down voluntarily.

The suspension was temporary until the conclusion of the case, he added.

Buhari's opponents have questioned the timing of the charges against Onnoghen so close to elections at which the president is seeking a second term of office.

The 76-year-old head of state, of the All Progressives Congress, came to power in 2015 on a pledge to tackle corruption.

International and domestic observers have already warned that the two main parties may attempt to rig the vote, in what is expected to be a close race.

The main opposition candidate Atiku Abubakar said Buhari's suspension of Onnoghen was "a brazen act of dictatorship" in a clear reference to his army past.

Buhari headed a military government in the 1980s.

Members of the Nigerian Bar Association were meeting on Monday to discuss the suspension, amid mounting protests that could lead to a court shutdown.

The NBA has called Onnoghen's removal "an attempted coup against the judiciary".

In another potential clash between the arms of government, parliament has been recalled on Tuesday for an emergency session.

Buhari's critics, including the Senate leader Bukola Saraki, have previously alleged he has used state security agencies to target perceived political opponents.

The president has been accused of conducting a political witch-hunt, as most of facing corruption charges are opposition lawmakers.

Onnoghen is facing trial at the Code of Conduct Tribunal, where Saraki was also brought on charges of failing to disclose his assets. He was cleared by the Supreme Court.

Under Nigeria's constitution, the Senate has to approve a motion to remove the chief justice by a two-thirds majority.

Analyst group SBM Intelligence said the only previous case of a chief justice being removed was in 1975, after general Murtala Muhammad ousted Yakubu Gowon in a coup.

It said only the National Judicial Council, the advisory and regulatory body for judges, had the power to suspend a judicial officer.

"The motives of the president are fully political and in full force to influence the appointments of the election tribunal" that would rule on any disputed results, it added.

Onnoghen had been due to constitute the tribunal on Saturday.

Buhari's defence that he was acting in the national interest would have an impact on the rule of law, as well as political and economic uncertainty, SBM added.