Lagos, Nigeria (CNN) Nigerian President Muhammadu Buhari has come under intense scrutiny for suspending his country's Chief Justice just weeks before a general election, a move that critics have attacked as tyrannical and unconstitutional.

Buhari defended his decision on Twitter, saying corruption allegations against Chief Justice Walter Onnoghen -- who has been accused of failing to disclose bank accounts in foreign currencies -- are "grievous."

But the move was labelled a "coup against democracy" by the President of the Nigerian Senate, and prompted an outcry from the country's major opposition party, which halted its presidential election campaign temporarily in protest.

Describing the action as a "dangerous and brazen assault on the constitution," the Campaign Council of the opposition People's Democratic Party (PDP) said Friday that there was no point in campaigning in an election whose basis has been so flagrantly undermined.

"When democracy comes under this kind of virulent attack, then the election itself becomes superfluous," the statement said.

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