The UK has suspended Iranian airline Mahan Air's operating permit on safety grounds, the Department for Transport (DfT) has said.
The DfT said Mahan had been involved in incidents which suggested a poor level of operational control and planning.
It also cited poor safety control, including some aircraft operating without collision avoidance systems.
Last month the airline increased the regularity of its flights from Tehran to Manchester to five times a week.
Mahan, whose network spans 21 destinations in 10 countries, is based in the Iranian capital.
"We'll work with EU and other partners to help Air Mahan to rectify any deficiencies, but we won't allow them to recommence operations until they have convinced us they can do it safely," the DoT said.