The Citizens currently occupy sixth place in the table after two wins, a draw and a loss in their first four games, and the Ivorian has acknowledged that their title rivals have strengthened their squads since the end of last season.
Toure told BBC Sport: "Chelsea have started very well and there is no doubt that Liverpool are a fantastic team but Manchester United have signed a few great players and Arsenal are also have a fantastic team.
"We know it is going to be tough this year and we have to try to be as strong as possible. We won the Premier League last season but that is now in the past and we have to focus on improving and being more consistent.
"As champions we want to win it again so we have to work hard because all the other teams are going to come at us and try to beat us. We need to deliver."
Manchester City face table-topping Chelsea this afternoon at the Etihad Stadium.