Kenyan opposition leader Raila Odinga has pulled out of October's election re-run.
Mr Odinga said his withdrawal would give the electoral commission enough time to introduce reforms that will help deliver a more credible election.
The Supreme Court annulled the result of the original 8 August poll, which saw Uhuru Kenyatta declared winner, after finding irregularities.
But Mr Kenyatta says he is ready to proceed with the new vote as planned.
The country's electoral commission said Mr Kenyatta had won the August vote by a margin of 1.4 million votes - or 54% of the total, compared to Mr Odinga's 44%.
Kenya's vice-president, William Ruto, has now called on the commission to declare Mr Kenyatta president as a result of Mr Odinga's announcement.
The election re-run was due to take place on 26 October, but Mr Odinga said on Tuesday: "We have come to the conclusion that there is no intention on the part of the IEBC [electoral commission] to undertake any changes to its operations and personnel... All indications are that the election scheduled for 26 October will be worse than the previous one."
As a result, he said, "considering the interests of the people of Kenya, the region and the world at large" it was best that he withdrew from the race.
Mr Odinga's coalition party believes the election will have to be cancelled as a result of his withdrawal, allowing "adequate time to undertake the reforms necessary to conduct an election that is in strict conformity with the constitution, the relevant laws and the constitution".
But Mr Kenyatta, speaking at a rally in the southern town of Voi, said: "We have no problem going back to elections. We are sure we will get more votes than the last time."
He added: "We are also telling him it is the people's right to choose their leader. It is their sovereign right to choose their leader of choice."
Mr Odinga's opposition coalition - the National Super Alliance (NASA) - has previously made clear its participation in the election was contingent on reforms being made.
But Kenya's Independent Electoral and Boundaries Commission (IEBC) says it has made the necessary changes.
Prominent opposition senator James Orengo has called on people to protest on Wednesday, using the slogan "no reform, no elections".
Administrators closed Kenya's oldest university on Tuesday, citing fears for students' safety in a planned protest over police beatings at a campus demonstration last week.
Kenyan police frequently face accusations of brutality and extrajudicial killings from civilians and rights groups, but officers are rarely charged and almost never convicted.
Despite this, Kenya, an economic and transport hub in East Africa and a key Western ally in a volatile region, receives substantial financial support for its security services from international donors, including the United States and Britain.
Rights groups say at least 28 people were killed, mostly by police, in unrest following the August 8 election, whose results were later nullified by the Supreme Court due to irregularities.
A re-run of the presidential vote is scheduled for October 26 and the conduct of the police will be closely watched.
On September 28, University of Nairobi students protested against the arrest of an opposition lawmaker. Police responded by entering dormitories and classrooms, dragging out students, beating them with clubs and firing tear gas, according to a Reuters witness. The university said 27 students were injured.
A police spokesman did not respond to requests for comment but a presidential spokesman told local radio on Monday that robbers were hiding among the students.
On Tuesday, students had planned to demonstrate against the beatings but instead administrators shut down the university.
"The (University of Nairobi) Senate has decided to send the students home for their (own) safety," John Orindi, the university's corporate affairs director, told Reuters.
On Tuesday morning, riot policemen stood near a truck with water cannon outside the campus gates.
A 20-year-old veterinary student who did not want to be named for fear of retribution said students wanted the vice chancellor to resign "for allowing anti-riot police to enter campus and seriously injure students".
University officials had talks on Monday with the interior minister, police chief and the head of a Kenyan government watchdog that is charged with investigating complaints against the police.
Kenya's Supreme Court has blamed the country's electoral commission (IEBC) for its decision to annul the re-election of President Uhuru Kenyatta.
The judges said the 8 August poll was "neither transparent or verifiable".
Deputy Chief Justice Philomena Mwilu said the IEBC did not verify the presidential results before they were announced.
Mr Kenyatta got 54% of the vote against opposition leader Raila Odinga's 44%, according to the IEBC's results.
Mr Odinga went to court alleging that he had been cheated of victory and that the IEBC had not followed the law in the conduct of the election.
The Supreme Court took the unprecedented step of annulling the election on 1 September but it has only now explained why it took that decision.
It was the first time in Africa that a court had agreed with an opposition demand to cancel a presidential election over rigging allegations.
While the judgement was being read out, police fired tear gas outside the Supreme Court to disperse opposition supporters who had gathered to support Mr Odinga.
At one point a swarm of bees attacked some of them.
Ms Mwilu said that the commission had not complied with a court order to allow its electronic voting system to be scrutinised.
She said that the IEBC's refusal to comply with the order to grant access to its electronic voting system led the court to "accept claims by the opposition that the computer system had been infiltrated and compromised and the data interfered with, or that the IEBC officials interfered with the system themselves".
The electoral commission has disputed that its system was tampered with.
Opposition coalition Nasa has been pushing for the sacking of IEBC officials whom it blames for bungling the polls, saying that a new team should be in charge of the re-run scheduled for 17 October.
Doubts have however been cast on this date because OT-Morpho, the French company that provided the voting kits, has said that it needs to reconfigure the more than 40,000 kits and that the process would not be complete until at least the end of October.
The judges had ordered the re-run to be held in 60 days.
Four judges voted to annul the election while two dissented. Another judge was taken ill during the hearing of the petition and did not take part in the case.
A 14-year-old Kenyan girl was charged on Wednesday with multiple counts of murder for allegedly starting a fire at a Nairobi school dormitory that left nine other schoolgirls dead.
According to a source inside the court, where proceedings were held in camera due to the age of the accused, the girl denied starting the fire on September 2 at the Moi Girls High School.
A source close to the investigation, speaking on condition of anonymity, said they had discovered a WhatsApp messaging group on the suspect's phone in which she had mentioned her plans to burn down the school.
"I will burn the school," read one of the messages.
The girl appeared to be angry that her parents had sent her to Moi Girls instead of her preferred high school.
The bodies of the girls who died in the blaze were burnt beyond recognition and were identified only through DNA analysis, which was completed on Tuesday.
Opposition MPs in Kenya have boycotted the opening of the new parliament to protest against President Uhuru Kenyatta's decision to address it after a court annulled his election win.
They say that parliament should not have been convened until after the election re-run slated for 17 October.
The MPs instead joined opposition leader Raila Odinga for a campaign rally in the capital, Nairobi.
Mr Kenyatta said he still had the power to convene parliament.
"The set term of a president is embedded until a new one is sworn in as per the constitution," he told lawmakers.
"I want to assure every Kenyan and the world that every arm of government is in place and operational," he added.
Mr Kenyatta was declared winner of the 8 August poll, garnering 54% of the vote against Mr Odinga's 44%.
Mr Kenyatta had dared opposition MPs to skip the opening of parliament saying that his Jubilee Party had enough MPs to carry on with parliament's activities.
Only one MP from the opposition was present, according to Kenya's privately-owned Star newspaper.
The Standard publication reports that Supreme Court judges, who traditionally attend the official opening of parliament, were absent.
Chief Justice David Maraga's office however told the BBC that the judges had not been invited.
The judges are expected to make public their written judgment explaining why they annulled Mr Kenyatta's win before the end of next week.
A majority of the six judges who listened to the election petition ruled that there had been some "irregularities and illegalities" in the election.
Mr Kenyatta, who has been critical of the judges, said in his parliamentary speech that their decision had overturned the voters' will.
He also repeated his strong disapproval of the ruling but said he respects it.
He said that he had a track record of respecting the justice system: "I have previously demonstrated this before, when I conceded defeat in 2002 and heeded summons from an international court [ICC ] when I knew I was facing trumped up charges."
His initial reaction to the 1 September ruling was however scathing, with him calling the Chief Justice and his five colleagues " thugs" and promising to "fix" the court after the re-run election.
He was widely condemned for the comments but he has maintained that he has a right to criticise the court.
Meanwhile, Mr Odinga repeated his threat to boycott the election re-run unless some officials of the Independent Electoral and Boundaries Commission ( IEBC), which is in charge of elections, are fired.
He accuses them of deliberately interfering with the electoral systems to favour Mr Kenyatta.
IEBC chairman Wafula Chebukati told a press briefing on Tuesday that the commission was reviewing its structures to ensure that it is ready for the re-run election.