Various witness reports from Saturday suggested several people were killed during demonstrations that broke out in opposition strongholds after the announcement of the election results on Friday evening.
The Kenya Human Rights Commission meanwhile said it counted 24 deaths since Tuesday's election, most of them in the capital, Nairobi.
The police were "personally responsible for violations of Kenyan and international human rights law" in their treatment of those protesting the election result, the opposition coalition NationalSuper Alliance (NASA), which alleges electoral fraud, said during a press conference in Nairobi.
"This state terror is being executed following a very meticulous preparation," said NASA member James Orengo. "They knew they would steal an election, so all the instruments were put in place."
Orengo was however unable to specify the source of the death toll of 100 people, but said 10 of the dead were children.
The government on Saturday said that it had no information to suggest that anyone died in the protests.
"Police have not used live bullets on peaceful protesters," said Interior Minister Fred Matiang'i.
However he also described some of the protesters as "opportunistic criminals and looters" who had to be "dealt with," claiming they were attempting to use the fluid political situation to engage in criminal activity.
Opondo Kaluma, a lawmaker from protest-hit Homa Bay, said the security forces who put down the demonstrations in his area were not regular police officers but from the military.
In Mathare, a slum in the capital Nairobi, around 20 people were injured, with at least four suffering from gunshot wounds, humanitarian organization Doctors Without Borders (MSF) said.
Amnesty International meanwhile called on the Kenyan authorities to investigate reported fatal shootings.
"Everyone has a right to peaceful protest and they must not be hurt, injured or killed for exercising that right," Muthoni Wanyeki, the group's regional director for East Africa, said in a statement.
Amnesty said it had received credible reports that three people had been shot in the protests: one in Nairobi's Kibera slums and two in the western district of Kisumu.
Kenya's electoral commission announced on Friday that Kenyatta, who has been in office since 2013, won a second five-year term with 54.27 per cent of the vote. His rival, 72-year-old opposition leader Raila Odinga, secured 44.74 per cent of the vote.
Before the final announcement, representatives of Odinga's NASA walked out of the electoral centre in Nairobi, saying they were "not going to be party" to the announcement because their concerns about the vote's legitimacy were not "adequately addressed."
Tuesday's elections in Kenya were dogged by fears of unrest.
In 2007, many people believed Odinga was cheated of victory, and 1,200 people were killed in the violence that followed.
Armed Kenyan police run to disperse protesters in the Kibera slum in Nairobi
Kenya's opposition on Saturday said 100 innocent Kenyans were killed in post-election violence, while the government denied police used live ammunition to quell protests after the re-election of Kenyan President Uhuru Kenyatta.
