Iranian officials "have not determined yet to join the meeting" and have "made no decision" on joining a cap, the spokeswoman said as quoted by the Wall Street Journal.
Asked if production would reach pre-sanctions level by late September, she said "we don't think so."
On June 2, OPEC members discussed freezing oil output following the Doha meeting in April after OPEC and major non-OPEC oil producers failed to agree on freezing oil output at January 2016 levels to shore up prices.
OPEC members are reportedly scheduled to meet in October.