Lionel Messi has admitted that Argentina have so far failed to show their true ability at the World Cup.

The Albiceleste, who held on to beat Bosnia-Herzegovina in their opening game, needed a late goal to see off Iran earlier today to cement top spot in Group F.

"We are first, but we know this level of performance is not as good as we can give," Messi is quoted as saying by Goal.com.

"Iran closed down well at the back and we really struggled to find space. Still we created a lot of chances. Luckily we got the win in the end and got the points, but we have to keep improving."

Argentina round off their group stage campaign when they take on Nigeria on Wednesday afternoon.