During a meeting on Iraq's future in Baghdad two months ago, mid-level US and Iranian officials did meet briefly and discuss Iran.
Mid-level officials also met briefly at last weekend's Iraq summit at an Egyptian resort.
"Iran has agreed to this (negotiation) after consultation with Iraqi officials, in order to lessen the pain of the Iraqi people, support the Iraqi government and establish security and peace in Iraq," the agency quoted Mohammad Ali Hosseini, spokesman of Iran's foreign ministry, as saying.
The report said the negotiations will be held in Baghdad.
"Time and level of negotiation team will be decided by the end of the week," Hosseini was quoted as saying.
Last week, Hosseini said Iran was willing, under the right conditions, to improve its chilly relations with the US despite having passed up the opportunity for high-level, direct talks at the second Iraq conference.
US officials said before the conference that any meeting with the Iranians would be limited to the subject of Iraq.