The plane, operated by Sweden-based Nordic Airways, had just taken off from Sulaymaniyya on its way to Stockholm when crew members saw that somebody was firing at the aircraft.
"The pilots saw bright light and were under the impression that somebody was shooting at the plane," said Anders Lundblad, spokesman for the Swedish Civil Aviation Authority (Luftfartsstyrelsen).
It has so far not been confirmed that the plane was shot at. The aircraft, an MD-83, was not damaged. It landed at Arlanda on Thursday without the passengers noticing that anything was amiss.
Nordic Airways has cancelled all flights to northern Iraq for an indefinite period. The airline operates a weekly service from Stockholm to Sulaymaniyya.
"We are waiting for a new evaluation of the security situation in the area. We have asked the Foreign Ministry to draw up such an evaluation," said Mikael Wångdahl, CEO of Nordic Airways.
The aircraft crew was shaken by the incident. They have been offered a basic form of crisis therapy.
"We sat down and talked about the incident in a group," said Wångdahl.