The 59-year-old has resigned from the Worcestershire County Council Stourport seat he won just 13 days ago following the incident.
It comes as police revealed they had quizzed a man from Stourport
over the comments and seized a computer.
Father-of-four Mr Kitson today apologised after a series of anti-Semitic and anti-Islamic posts were discovered on his Facebook page, saying he was sorry for "letting down" his friends, family and constituents.
West Mercia Police confirmed officers were investigating after concerns were raised by members of the public.
In a statement today, Mr Kitson said: "It is with sadness that I am announcing my resignation as a councillor," he said.
"I am extremely sorry to have let down my friends, the people in the hardworking UKIP team that got me elected, the people of Stourport-on-Seven who gave me the honour of electing and of course my family.
"Like many people who are not professional politicians, I used my Facebook page as a general post board. That was foolish. I am no racist, but I can understand why people could think so."
A West Mercia Police spokeswoman said: "A man from Stourport was voluntarily interviewed by officers over concerns raised by the public about allegedly offensive and racist comments made on social media.
"A computer was also seized by police with the man's consent for evidence gathering purposes."
"An investigation has now been launched by West Mercia Police into the complaints and officers will establish whether any offences have been committed."
Today, UKIP officials said they will continue to investigate the incident and confirmed Mr Kitson's membership would be considered by the National Executive Committee.
UKIP chairmam Steve Crowther added: "We believe that Mr Kitson is an honest man who has made, by his own admission, some serious mistakes, by posting or reposting offensive material on his Facebook page which he should never have associated himself with. He regrets this enormously, and rightly so.
"His decision to resign is, under the circumstances, the right one."