President-elect Barack Obama says the United States will take a new approach to dealings with Iran under his leadership.
Mr Obama said in a television interview screened in the US on Sunday that "Iran is going to be one of our biggest challenges".
He said he was concerned about Iran's support for Lebanese Shia party Hezbollah and Tehran's nuclear enrichment programme.
In the wide-ranging interview, Mr Obama also said he planned a special team to deal with conflict in the Middle East.
He said he was not ruling out prosecution for possible crimes committed by Bush administration officials.
And he repeated his promise to close the Guantanamo Bay prison camp, but suggested it might not happen within his first 100 days in office.
Mr Obama also criticised the Bush administration's handling of the $US700 billion federal bailout plan to help the US banking system amid the global financial crisis.
He said his attorney general could investigate accusations Bush administration officials had abused their power.
Mr Obama, who won the US presidential election in November, takes office on 20 January.