The president of Kenya, Uhuru Kenyatta, has said his country has "a problem" with its judiciary after the Supreme Court cancelled his victory in last month's presidential election.
Speaking on live television, he vowed to "fix" the court if re-elected.
It comes a day after the Supreme Court cited irregularities in the vote and ordered a new one within 60 days.
Mr Kenyatta has said he will respect the ruling and called for calm amid fears of unrest.
But at a rally in Nairobi on Friday he branded the Supreme Court judges "crooks".
The 8 August poll raised fears of major violence similar to that following a disputed vote in 2007.
Deputy President William Ruto has called on the electoral commission to set a date for fresh presidential elections, saying the governing Jubilee Party is ready.
But opposition candidate Raila Odinga wants the commission replaced, saying it has lost credibility.
It is believed to be the first time in Africa that a court has ruled against the electoral win of an incumbent based on a court challenge by the opposition.
"We shall revisit this thing. We clearly have a problem," Mr Kenyatta said of the judiciary during his television address on Saturday.
"Who even elected you? Were you? We have a problem and we must fix it."
Although the unrest in this year's vote was not as serious as in 2007, days of sporadic protests left at least 28 people dead.
Kenya's election commission had declared Mr Kenyatta the winner by a margin of 1.4 million votes but the result was immediately challenged in court by his nearest rival, Mr Odinga.
In a ruling on Friday, Chief Justice David Maraga said the 8 August election had not been conducted in accordance with the constitution, declaring it "invalid, null and void".
The ruling did not attribute any blame to President Kenyatta's party or campaign.
Mr Odinga, 72, said the ruling marked "a historic day for the people of Kenya and by extension for the people of the continent of Africa".
Following the election, international monitors from the EU, the African Union and the US had said there was no major fraud and urged Mr Odinga to concede.