flat-out deny

Translations
категорически отрицать
He flat-out denied any involvement in the incident.
Он категорически отрицал любое участие в инциденте.
Definitions
To completely and unequivocally refuse to acknowledge or accept something, often in a blunt or straightforward manner.
Words
deny

verb
отрицать
flat-out

adverb
напрямую