Iraqi and U.S. officials say Iran has postponed an expert level meeting with U.S. representatives on improving Iraq's security situation.
Tehran has not given a reason for the decision and no new date has been set.
The Associated Press news agency quotes U.S. embassy spokeswoman Mirembe Nantongo as saying it is increasingly clear that Iran is not ready to sit down for talks.
The meetings were scheduled to be in Baghdad on Friday. They were going to be the fourth round of talks on the security situation in Iraq.
U.S. and Iranian officials met three times in Baghdad last year, breaking a 27-year freeze in diplomatic contacts between the two sides. Two of those meetings involved U.S. Ambassador to Iraq Ryan Crocker and his Iranian counterpart, Hassan Kazemi Qomi.
In another development, Iranian President Mahmoud Ahmadinejad will travel to Iraq on March 2 for a two-day visit. The planned visit will be the first by an Iranian leader to Iraq in years.
Some information for this report was provided by AP and Reuters.