Direct flights between Iran and Serbia have resumed after a gap of 27 years with the landing on March 10 of an IranAir jet at Belgrade's Nikola Tesla Airport.
With the resumption, some groups in Serbia have raised concerns that the flights might be used as a new route for migrants from Iran looking to remain permanently in Europe.
All flights on IranAir's twice-weekly Tehran-Belgrade service have been fully booked until the end of the summer, Serbian media have reported.
Qeshm Air, another Iranian airline company, is also planning to launch a service between the countries on March 19.
The service was widely anticipated ever since Serbia signed a visa-liberalization deal with Iran in August 2017. Many of those flying on the service are expected to be Iranian nationals living in Europe.
However, Info Park, a Serbian refugee-support group, has warned that the flights could be become a new migrant route for those seeking to stay in the EU illegally.
Since visa requirements were lifted, the Serbian Trade Ministry said some 7,000 Iranians have traveled to Serbia, with about 485 applying for asylum.
Info Park said a number of Iranians had legally arrived in Belgrade as tourists, but moved to EU countries, mainly France and Germany, instead of returning to Iran.
"Although they entered Serbia as tourists, interviews have revealed that many Iranians use their stay in Belgrade to establish connections with smugglers, who will transfer them to their desired destination, across the borders of Croatia, Bosnia-Herzegovina, Hungary, or Romania," Info Park said at the time.
The group said those leaving Iran cited a variety of reasons, including concerns about their political, religious, or sexual-orientation rights.
"Seeing as most of these new-arrivals do not intend to return, the migration systems in Europe must recalibrate for this new route and demographic among the migrant populaces," it said.
Serbian Trade Minister Rasim Ljajic said both countries' authorities would investigate any possible abuses of the system, with checks reinforced in Tehran.