He stated this on Tuesday at the emergency National Executive Committee (NEC) meeting of the PDP in Abuja, where he also urged Nigerians not to despair.
The former Vice President also asked the military and other security agencies not to obey unlawful orders.
“When you people are talking about democracy, I have always said that General Muhammadu Buhari is not a democrat. He has never been a democrat. We started the fight to drive the military away from governance, he was never there. He never participated.
“I am sure that you have followed with interest, utterances from the leadership of the All Progressives Congress, and General Muhammadu Buhari in particular which are a painful reminder of the era of dictatorship and military rule. General Buhari has consistently violated the constitution; he failed to uphold the rule of law.
“Only yesterday (Monday), General Buhari said and I quote, ‘The military and police should be ruthless. Anybody who disturbs the voting system will do so at his own risk’ that is General Buhari.
“It is shocking for any head of state to utter such words in a democracy and we shall not accept it from General Buhari in this country. We have fought more ruthless dictators than him,” Atiku said.
He also alleged that the ruling All Progressives Congress (APC) had equipped many of their members with unnamed devices that could slow down or quicken the Smart Card Readers during the presidential poll.
He accused the governing party of doing that in some geopolitical zones where the APC allegedly believed it would never win.
“So, if you are in the South-South, South-East and North-Central, you are likely to get your card readers to be slowed by those APC operatives.
“We have seen the machines; we have interviewed some of those who have gone on this training, and we have passed that information to the campaign council to pass to you.
“But if you are from the North-West or North-East the tendency is that they will use these machines to fast-track the reading of your card readers, so that many of their supporters can vote while disenfranchising the other three zones,” he said.
He said Buhari must ensure the presidential poll was free, fair and credible, adding that if he does so and wins, “then the people will commend you for it but otherwise, history will condemn you for it but before history does that, we will condemn you for it.”