Iran's official news agency is reporting that Tehran has secured S-300 anti-aircraft missiles from Belarus. I am...skeptical.

Col. Sam Gardiner is too. He notes:

The S-300 is 20-year old technology but has been a major item for the Russians on the international arms market.  Russia has shown restraint in not fulfilling the contract it has with Iran to deliver the S-300.  Iran has been very vocal in its protestation.  Belarus does have the S-300.  Despite their differences, Russian and Belarus do work closely on air defense.  It is unlikely Russia would allow Belarus to withdraw missile from their collective air defense network.

The important capability of the S-300 is that it is a system to integrate air defense.  It is not just about the missile.  The system includes radar, processing capability and mobile command center.  Belarus is unlikely to have sold Iran a system.  Even if Iran were able to obtain a few missiles, it would be an insignificant military capability.

Speculation is rampant about what it all means. The Iranians, presumably, believe that the weapons have military utility, or that people will think that they do. Nukes of Hazards has an interesting take.