This according to Disney's Robert Iger. Via The Hollywood Reporter:
The Avengers was made official Tuesday by Disney CEO Bob Iger, who made the announcement during a conference call with analysts to discuss quarterly earnings.Anybody surprised? The Avengers is kicking some major box office but so it should be no surprise. Iger also reiterated some previously released news about the individual movies.
Iger said a third Iron Man and a second Thor are scheduled for 2013 and a sequel to Captain America: The First Avenger is in the works for 2014. He gave no timeline for an Avengers sequel.