Barham Saleh, Iraq's deputy prime minister, said the talks will go ahead but did not give a specific date.
Tom Casey, the US state department's deputy spokesman, said Washington had not received any confirmation from the Iraqi government about the meeting.
The Associated Press news agency quoted an unnamed official as saying that the Iranian delegation, which arrived in Baghdad on Wednesday after the talks were announced, would return to Tehran after visiting Shia Muslim shrines in Baghdad and in Karbala.
Tehran has enjoyed increasingly friendly relations with the Iraqi government, many of whose members spent time in Iran while Saddam Hussein, Iraq's former president, was in power.
Mahmoud Ahmadinejad, Iran's president, recently completed a visit to Iraq, stressing his government's closeness to Baghdad and criticising US influence in the Middle East.
During the two-day trip, Ahmadinejad said that American power in the region was divisive and asked foreign powers to leave the country.