Iranian Foreign Ministry spokesman Ramin Mehman-Parast told the semi-official Fars News Agency that the visit was "postponed to another time," adding that the Majlis (the Iranian parliament) was determining a new date for the visit.
Fars reported that Mehman-Parast said that the visit was "postponed due to the necessity of advance planning to maximize constructive and mutual parliamentary cooperation between the two sides."
The EU parliamentarians, however, said Tehran's decision caught them by surprise.
In a statement released from Brussels, delegation chairwoman Barbara Lochbihler, a German Green Party MEP, said group planned to talk about the recent political upheaval in Iran and "state repression."
She added that the visit was to include not only official exchanges with the Majlis, "but also a wide range of meetings with the political opposition and representatives of civil society."
The postponement, Lochbihler said, was "another sad illustration of how much the Iranian leadership opposes any discussion of the major unresolved problems in the country."