Star striker Ibrahimovic, 25, will now receive five million euros per year instead of four.
"It's simple: Inter contacted me and asked if I wanted to extend my contract until 2012 - and I said yes," Zlatan told Corriere dello Sport.
"I want to make one thing clear: I did not ask for anything. My agent [Mino Raiola] and Inter's bosses reached a deal."
Zlatan added that despite offers from Chelsea and Real Madrid, he never considered leaving Italian champions Inter.
"Absolutely not," he responded. "I like it here and I don't think about anything else. I believe in Inter and I know that we will succeed.
"My family also likes it in Milan and we bought a nice house a month ago. Everything is great; the only thing missing is [Roma star Cristian] Chivu."
Inter coach Roberto Mancini wants to take Romania left-back Chivu to the Giuseppe Meazza, but Roma - who finished second in Serie A last season - are unhappy about allowing him to move to their rivals.
Ibrahimovic failed to score in the Champions League last season as Inter went out to Valencia in the second round on away goals, but is determined to put that right in the coming campaign.
"I don't know why I didn't score in Champions League," he said. "I always try to give my best; maybe I'm luckier in the league.
"The Champions League is important, even more so this year. I must do better and I will succeed."