Messi has won a host of top honours with Barça but has yet to taste major success with the Albiceleste, who are without a top title since 1993 and flopped at the Copa America on home soil in July, with many observers puzzled as to why his club form rarely appears at international level.
"I still have this dream and that is to be a world champion and lift the Copa America with the national side. And I know I'll do it, I am convinced I shall," insisted Messi.
"I don't have to demonstrate anything to anybody. I would love to win a title with the national team but I am just another one in the group who wants to do the best for Argentine football, nothing more," he added.
Under new coach Alejandro Sabella, Argentina got off to a mediocre start in their 2014 FIFA World Cup qualifiers with an embarrassing loss to Venezuela, but their recent win over Colombia put them on a more even keel and they are now level on points with regional group leaders Uruguay, albeit having played a game more, and Venezuela.
"The group are doing fine. But we needed a win like that to strengthen ourselves. It has revitalised us," Messi said, recognising that "sometimes we don't quite get up to the mark either in terms of performance or the result. We are aware of that."
On the difference between playing for his country and Barça, with whom he has just won the FIFA Club World Cup, Messi said: "They are two different things. Barcelona are the best team in the world, even non-fans admit as much. That is the result of years of hard work with the same team-mates.
"It's more difficult with the national side and we've been through a lot of chopping and changing of coaches in recent years," he said pointedly. "But we are growing and I know we are going to achieve a lot."