'Losing it'
Ruto's comments have been met with shock and anger by parts of the population.
"The president is losing it," wrote Kenyan newspaper The Standard in an editorial, with another frontpage that read: "Kenya sliding into tyranny".
"Whether he's instructing police to shoot in the leg or wherever... let us just take it for what it is," said Otsieno Namwaya, a researcher with Human Rights Watch.
"It is a shoot-to-kill order," he added.
Karuti Kanyinga, a political researcher at the University of Nairobi, said the government's heavy-handed response to protests reminded him of the 1990s, when Kenya suffered years of autocratic rule by then-President Daniel arap Moi.
Ruto himself has said he is a "student" of the former leader, cutting his political teeth in the youth league of Moi's party.
"We are on a cliff and the possibility of going to a very violent period, like the post-election violence period of 2007, is very high," said Kanyinga.
"I think he's preparing to move into a tougher, repressive phase in his regime," he said of Ruto.
'Dictatorship 101'
Pro-democracy protests last week to mark Saba Saba day -- the anniversary of the bloody 1990 uprising that demanded a return to multi-party democracy after years of autocratic rule -- were met by a heavy police presence and violence.
Rights groups reported at least 38 deaths among protesters, while the government says only 17 people died.
"Saba Saba was the deadliest single day since the beginning of the demos" a year ago, said Africa Hussein Khalid, head of rights group Vocal.
Protests also erupted in June over the death of teacher Albert Ojwang, who died in custody, with people marching in Nairobi against police brutality.
The United Nations has condemned the use of force by Kenyan authorities.
Contacted by AFP, a government spokesperson pointed to Ruto's full remarks last week to "understand the context", without answering further questions.
But for many rights defenders, Saba Saba marked a new low.
"Ruto defended the police without saying a single word for the victims," Khalid, from Vocal, said.
"The force is used to silence dissent," he said. "It is dictatorship 101."