Denver, Aug. 10 (Reuters): Grammy-winning singer-songwriter Taylor Swift testified today she was subjected to a "very long" and "intentional" grope by a Colorado disc jockey who appeared to be drunk during a photo session four years ago.

The 27-year-old pop star was testifying for the first time to a federal court jury weighing her accusation that David Mueller grabbed her during a pre-concert fan reception in 2013 against Mueller's assertion that she falsely accused him and got him fired as a result.

Swift, one of the US's most popular performers, spoke forcefully under questioning by Mueller's attorney, Gabriel McFarland, saying several times that "your client grabbed my ass", at one point calling it a "devious and sneaky act".

Mueller, 55, testified on Tuesday that he may have made innocent contact with Swift but denied any inappropriate behaviour. Asked if he grabbed her, the former disc jockey for Denver radio station KYGO-FM replied,"No, I did not."

Swift, who spent an hour on the witness stand today, said it appeared both Mueller and his girlfriend, who stood on the other side of her for the photo, had "had a few cocktails".

Asked by McFarland why her bodyguard did not step in when "this big drunk guy" groped her, Swift replied: "No one could have expected this to happen.... It had never happened before. It was horrifying and shocking."

Questioned by the attorney as to whether it might simply have been a case of mistaken identity on her part, she fired back: "He had a handful of my ass. I know it was him."

Asked about her reaction when she learned that Mueller had been fired, Swift replied,"I just never wanted to see him again. And here we are years later and I'm being blamed for the unfortunate events in his life," referring to the DJ losing his job. Mueller initiated the litigation, arguing that Swift had fabricated the story.