Ferguson has been infuriated by comments from Patrick Vieira, City's football development executive, who this week said the United boss's decision to bring Paul Scholes out of retirement was a sign of desperation.
Former City and Arsenal midfielder Vieira was shocked that Ferguson turned to Scholes to bolster his midfield in January after the 37-year-old spent several months in retirement.
However, United have won nine Premier League games with Scholes in the team to replace City at the top of the Premier League.
City closed the gap on their bitter rivals with a win over Chelsea on Wednesday, but Ferguson took the chance to hit back in a week when Carlos Tevez made his controversial return to Mancini's team six months after he refused to warm-up during a Champions League game at Bayern Munich.
"Desperation? Paul Scholes is the best midfielder for the last 20 years, Ferguson said on Friday.
"Roberto Mancini had a little dig at us a couple of weeks back. We are all going to play our hand. I have plenty of ammunition that way.
"Desperation? On Wednesday they played a player who refused to go on the pitch and the manager had said would never play for them again. What is that?"