Several mysterious cargo planes from China have flown near Iran’s airspace before disappearing from radar, raising concerns that Beijing may be covertly supporting the conflict, according to reports.

Public flight trackers revealed at least three Boeing 747 freighters—often used to transport military equipment and weapons—departing from Chinese cities on Saturday (the day after Israel struck Iran), Sunday, and Monday, according to The Telegraph.

Each plane flew west across northern China, crossed into Kazakhstan, then continued south through Uzbekistan and Turkmenistan before vanishing from radar near Iran.

Although the flight plans indicated Luxembourg as the destination, none of the aircraft seemed to head towards Europe, The Telegraph further noted.

“These cargos cannot but generate a lot of interest because of the expectation that China might do something to help Iran,” Andrea Ghiselli, a lecturer at the University of Exeter who specializes in China’s relations with the Middle East and North Africa, told the outlet.

Cargolux, the Luxembourg-based company operating the planes, told The Telegraph that their flights did not enter Iranian airspace but did not answer questions regarding the cargo.

China and Iran maintain a strategic partnership opposing the U.S.-led world order, with Beijing historically supplying Tehran with military equipment, including conventional arms and ballistic missile materials that could potentially be used in nuclear weapons development.

Since the 2000s, international sanctions have significantly reduced direct arms transfers, shifting the focus toward “dual-use” materials.