Nairobi - Kenya's opposition announced Wednesday it will challenge the results of last week's presidential election in Supreme Court and wage a campaign of "civil disobedience."Opposition leader Raila Odinga told reporters that Kenyans won't willingly go along with "democracy's slaughter."His comments had the potential to set off another wave of protests in the capital, Nairobi, and elsewhere that already have led to at least two dozen people being shot dead by police since the August 8 vote, according to one prominent Kenyan human rights group.Odinga has claimed that the election results were hacked and rigged in favor of President Uhuru Kenyatta, who won a second term. Kenya's election commission has said there was a hacking attempt but it failed, and election observers have said they saw no signs of interference with the vote.The opposition last week said going to court was not an option, but Odinga on Wednesday made it clear it is an option now."We will not accept and move on," he said. "We shall hold vigils, moments of silence, beat drums and do everything else to draw attention to the gross electoral injustices."Odinga's challenge after losing the 2013 election to Kenyatta was unsuccessful.Streets of Nairobi's populous slum of Kibera were empty ahead of Odinga's statements on Wednesday, with businesses closed as they awaited his announcement. The opposition stronghold has seen some of the worst clashes between police and civilians protesting the results after the electoral commission announced Kenyatta's win late on Friday.Also Wednesday, Kenya's Interior Minister Fred Matiangi stopped an attempt to de-register two civil society groups that pointed out anomalies in the presidential election.The National Non-governmental Organizations Board has said it de-registered the Kenya Human Rights Commission and called for the arrest of the directors of the Africa Centre for Open Governance. Both groups monitored the elections.In a statement, Matiangi said a committee will be formed to look into allegations that the two groups had tax compliance issues and one was not registered. He also ordered that no action be taken against the groups for 90 days.