"However, I have a genuine belief that we were making progress and that the players have what it takes to turn this season around."
Ipswich, backed by multi-millionaire Marcus Evans, have invested £8m on players during Keane's reign.
The former Manchester United midfielder led Town to the semi-final of the Carling Cup where they will play Arsenal.
The first leg of their last four clash against the Gunners is due to take place at Portman Road on Wednesday, 12 January.
"We were preparing well for our visit to Chelsea on Sunday and then our Carling Cup semi with Arsenal," Keane continued.
Clegg explains Keane sacking
"Getting to that semi proves what I know the team is capable of.
"I was also working hard to build the squad during the transfer window, looking at our options to attract new players to the club.
"I have loved my time at Ipswich, living locally to the club with my family, and have a massive respect for the club, its staff, the fans and the community and I wish them well."
Evans added: "I would like to put on record my thanks to Roy for his commitment to try and bring success to Ipswich Town."
And club chief executive officer Simon Clegg said: "Today is a sad day for me. I have enjoyed working with Roy over the past two seasons and I would like to thank him for his tremendous dedication and professionalism during that period.
"Regrettably though, we have not made the progress that we had all expected over the last 20 months and this season in particular with the side slipping to 19th place in the Championship table."
Clegg added the club hope to make a new appointment in the coming days, but said it was unlikely anything would happen before Sunday's game.
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