The clubs said they had been involved in negotiations over the players, who left Sampdoria during the 2010-11 season, although a deal had yet to be finalised.
"It's an interesting operation - who doesn't want a player like Cassano?" Inter president Massimo Moratti was quoted as saying on the club's website. "We think he can be useful and the coach thinks the same."
AC Milan broadcast an interview on their television channel with midfielder Riccardo Montolivo, welcoming Pazzini to the club.
"It will be wonderful if he arrives," said Montolivo, a former team mate of Pazzini's who was signed from Fiorentina earlier in the close season.
"Pazzini has done well in all the teams he played for. He is a fox in the penalty area, he's strong in the air and helps his sides to play well."
Media reports say Milan will pay an additional 7.5 million euros to their city rivals for Pazzini, 28, who scored only five goals in Serie A last season for Inter.
Cassano's departure from Milan comes as a surprise, given that he has revived his career in his 18 months at the club and become firmly established in the Italy line-up.
Having been overlooked for the 2010 World Cup, the 30-year-old formed Italy's strike partnership with Mario Balotelli at Euro 2012, despite missing six months of the season after undergoing minor heart surgery.
Cassano has had a colourful career marked by tantrums and personality clashes, but his early immaturities looked to have been ironed out when he joined Sampdoria from Real in 2007.
However, a verbal spat with the Sampdoria president Riccardo Garrone led to him being suspended in 2010 and he joined Milan where he became a key factor in their Serie A triumph last year.