Donald Trump has threatened to sue the Twitter troll who asked him to retweet a photograph of killers Fred and Rosemary West.

Trump tweeted the picture with the message "My parents who passed away said you were a big inspiration. Can you please retweet (the message and image) for their memory?" to his 2.7m followers yesterday after being targeted.

He has now hit back on the social media site and is threatening legal action against the troll who targeted him.

He tweeted: "Some jerk fraudulently tweeted that his parents said I was a big inspiration to them + pls RT-out of kindness I retweeted. Maybe I'll sue.

"I thought I was being nice to somebody re their parents. I guess this teaches you not to be nice or trusting. Sad!"

Twitter users were quick to pick up on the billionaire businessman's mistake yesterday, with Tom Eldridge tweeting: "Social media 101 lessons for Donald Trump. I would do some research before posting."

Fred West, who murdered at least 12 women between 1967 and 1987, killed himself in 1995 while awaiting trial. His wife Rosemary, who took part in most of the killings, is currently serving a life sentence.