International and U.S. extra-territorial sanctions against Iran are often credited with making travel on Iranian commercial airlines relatively unsafe. International companies won’t sell Iran spare parts for even routine maintenance on their fleet.

But a new potential side effect of energy sanctions against Iran are causing worries about more than just Iran’s domestic fleet of passenger aircraft.

Because of sanctions, international flights no longer refuel at Iranian airports. For European airlines, that means that they either have to depart with enough fuel for both legs of the long journey or add refueling stops to their heretofore direct flights.

A source in Iran recently forwarded me an e-mail from German carrier Lufthansa, Europe’s largest, making clear that though the airline intends to fill the tank for both legs, unscheduled stops may still be necessary. The message is clear: Please don’t be scared if we start to run out of gas on the way home!

The e-mail, with my emphasis, reads:

Due to non-availability of fuel from Tehran, following actions have been implemented by Lufthansa:

Lufthansa takes substantial additional fuel in Frankfurt on the flight leg to Tehran. This ensures Lufthansa aircraft have sufficient fuel for both the legs Frankfurt to Tehran and Tehran to Frankfurt. As such, there is no need for a change in our schedule and our flights Frankfurt-Tehran-Frankfurt operate nonstop in both directions.

Nevertheless, there might be very exceptional cases when additional fueling en route to Frankfurt might be required, in which case the pilot will make the decision to land at an airport on the way back to Frankfurt. We would, however, like to stress that such occasions are expected to be very rare.