Inter said last week they would not make any comment on the Tevez situation until after their Milan derby clash with rivals AC at the weekend.
The Nerazzurri won the game 1-0 and straight after the game manager Claudio Ranieri and the club were quizzed about the Argentine.
Ranieri would not be drawn closely on the issue, but Moratti has wasted little time in confirming that they have now made a firm offer of just over £20million.
"There are no secrets in football," Moratti told Controcampo.
"The offer is 25m euros. Now it is up to City whether they accept that bid or not."
Moratti also admitted they were not the only club chasing Tevez, with PSG and also English clubs in the hunt.
He added: "However, I do think that there are a number of other clubs who are interested in him. There are some English sides and also Paris St Germain."
The news of Inter's bid comes less than a week after AC withdrew from talks for Tevez after Alexandre Pato shunned a move to PSG.
"At this moment in time it seems that we don't need Tevez, but football gives a different answer on a daily basis," he continued.
"I would keep all of the players that are in the squad right now, but there is still time until the transfer window closes. We'll wait and see."