allege, veracity, vilify
Denise Richards alleged that Charlie Sheen threatened to kill her, but he argued against the veracity of her statements and claimed that she is simply trying to vilify him with a "most obvious immature and transparent smear campaign."
allege - (verb) to assert, usually without proof
veracity - (noun) truthfulness, accuracy
vilify - (verb) to lower in importance, defame
- Read more about words that mean "verbal attack"