The pictures were posted on the Facebook page of Michael Orita, who sources say is a senior police official in Kenya's north-eastern county of Garissa, the scene of the April massacre of nearly 150 students by Somalia-led al-Shabaab rebels.
The victims were identified in the Facebook post as Somali youths who had crossed the border into Garissa.
"These Somalia young men came to Garissa for a purpose but little did they know we are smarter than them, we shall not relent on security issues," the post says.
The photos show a group of around 10 young men face down on the ground while they are being whipped by what looks to be a rubber hose by a man in civilian clothes carrying an assault rifle.
Uniformed police look on and a marked police car is visible in the background.
Another picture appears to show another plain-clothes official trampling over the youths. The pictures were later pulled from the social networking site after an outcry over police brutality.
"How will the security agencies expect the local people to work with them while they torture people in this manner?" said Khalif Abdi, co-ordinator of the North-Eastern Forum for Democracy.
"What will stop the victims from harbouring resentment against their government and having a soft heart for terrorists?"
Garissa County police commander Shadarack Maithiay said an investigation was under way.
"The pictures have come to my attention and I have instructed the relevant agencies to speedily investigate their authenticity and whether the person claiming to be a senior police officer who posted them is a genuine member of our security force," he said.
Maithiay said he was unable to confirm if there was a Michael Orita in the local force.
But he added: "Even if we found we have such person in our force we can't conclusively say he is responsible without our investigation proving that."
"What is seen in the pictures is wrong. It is against the ethics and the code of conduct for any security force. I'm disturbed but it is good for us to be patient for our investigations to establish whether they are genuine," he said.
Quoted by The Star newspaper, Garissa County Commissioner James Kianda said those involved "will face disciplinary action, of course subject to validation."
"This is not how we want to fight terrorism," Kenya's national police chief Joseph Boinett was also quoted as saying.