The aircraft, registered EP-KPB, was due to depart Istanbul Airport when lawyers and enforcement officers representing ACM Temsil Gözetim, an aviation representation and supervision company, arrived at the aircraft and carried out the court-ordered seizure, according to Anadolu Agency.
The intervention left passengers stranded at the airport after they had already boarded the aircraft and prepared for departure. Cabin crew were also removed from the Boeing 737, with everyone subsequently returning to the terminal.
The seizure comes at an especially difficult time for Iran's aviation industry, with the country's airlines already facing severe financial and operational pressures caused by longstanding US sanctions.
It also occurred only days after new US secondary sanctions targeting Iran's aviation sector took effect, contributing to a sharp reduction in the number of international flights operating to and from Tehran.
Debt dispute brings flight to a halt
The seizure followed a claim by ACM Temsil Gözetim over approximately €3 million owed by the airline. Rather than allowing the aircraft to depart, Turkish enforcement officers boarded the Boeing 737 while it was still at the gate and served the relevant court order.
The action demonstrates the extent to which financial disputes involving Iranian airlines can affect operations outside Iran, particularly as carriers attempt to maintain international routes despite sanctions and restrictions on access to global financial and aviation services.
Passengers who had expected to travel to Iran were consequently left without their scheduled flight after the aircraft was prevented from departing.
Caspian Airlines, based in Tehran, was established in 1993 and operates as part of Iran's state aviation group. The carrier operates Boeing 737 aircraft on domestic and international routes, including services between Iran and Turkey.
Turkey has not imposed a formal ban on Iranian airlines, allowing carriers such as Caspian Airlines to continue serving Istanbul.
That distinction has allowed the route to remain operational even as other countries have moved to restrict or suspend services by Iranian carriers.
Iranian aviation hit by expanding sanctions
The seizure comes against the backdrop of decades of sanctions that have made it difficult for Iranian airlines to obtain aircraft, spare parts, maintenance services and access to international financial networks.
Those restrictions have contributed to persistent challenges in keeping Iran's ageing commercial fleet operational and meeting financial obligations to overseas companies.
The situation has become more difficult since the war between the United States and Iran began in February, disrupting Iranian airspace and forcing changes to international flight schedules.
A further blow came on 8 September, when the US Treasury announced sanctions against 27 Iranian airlines and nine associated service providers under its Operation Economic Outcast.
The measures also carried consequences for foreign companies doing business with Iran's aviation industry. Airports, fuel suppliers, ground-handling companies and ticketing firms that continued providing services to sanctioned Iranian carriers faced the possibility of being targeted themselves and losing access to the US dollar financial system.
The secondary sanctions quickly began to affect international aviation links.
Iranian carriers suspended flights to several destinations, including Iraq, the United Arab Emirates, Azerbaijan and Oman. Mahan Air, one of Iran's largest private airlines, subsequently suspended services to Turkey and Oman.
European carriers also reduced their operations. Lufthansa and Austrian Airlines suspended their services to Iran through 24 October, while Qatar Airways halted flights, citing airspace restrictions.
China, Russia and Pakistan have continued operating flights to and from Iran.
Tehran's international connections shrink
The impact of the restrictions has been reflected at Tehran's main airport, where international traffic has fallen sharply.
Tracking data showed that the number of international flights operating each day had dropped from approximately 80 to 90 before the latest sanctions to about 41 by Monday.
The reduction represents a significant contraction in Iran's international air links and leaves passengers with fewer options for travelling to and from the country.
Iran has formally protested the restrictions, filing complaints with the United Nations, the International Civil Aviation Organization and the International Court of Justice.
Tehran has argued that the measures are affecting civilian aviation and international connectivity, while the United States has imposed the sanctions as part of its broader pressure campaign against Iran.
Istanbul route remains open
Despite the wider disruption, Turkey has continued to allow Iranian airlines to operate, meaning Caspian Airlines was still able to maintain its Istanbul service when the Boeing 737 was seized.
The incident therefore stemmed not from a Turkish decision to suspend Iranian aviation, but from a separate legal action over the airline's financial obligations.
For the passengers who had already boarded, however, the distinction offered little immediate relief. Their flight was stopped before departure, with the aircraft remaining on the ground as the enforcement process was carried out.
The seizure adds another complication for Iranian carriers attempting to maintain international operations at a time when sanctions, airspace restrictions, financial pressures and fleet-maintenance difficulties are already reducing the country's access to global aviation networks.