Ahmadinejad, in Copenhagen for a UN climate change summit, said he had welcomed the "slogans" of change when Obama was elected US president a year ago but he had not lived up to expectations.
"He has not used the possibilities, making decisions similar to the previous (Bush) administration," he told a press conference.
"We see they are sending more troops to Afghanistan, that's a continuation of the policy of the former administration and the situation has not changed in Iraq and Palestine," he added.
Ahmadinejad said that there were "many politicians in the United States who see themselves as the masters and owners of the world", adding that Obama's behaviour had "made us concerned."
Obama came to power offering dialogue with Iran's hardline Islamic regime, but the administration's attitude has hardened in recent months over Tehran's nuclear programme.
The Obama administration has given Iran until the end of the year to seize its offer of engagement to end the stand-off with the focus now increasingly moving towards tougher sanctions against Tehran.
