Some 26,000 diamonds, worth at least $162,000 and contained in transparent plastic bags in hand luggage, proved too much for the "nothing to declare" lane at a Moscow airport.
An unemployed, 37-year-old Russian man carrying the precious package from Dubai was detained on Sunday at the international Sheremetyevo airport, Russia's federal customs service said.
"One customs officer noticed he was very nervous during regular luggage checks and was pressing a bag under his arm, so she asked him to let her see what was inside," spokeswoman Natalia Karaseva said.
The man, from the restive Dagestan region in Russia's North Caucasus, said he was carrying the diamonds as a favour for a friend. It was not clear whether he would face criminal charges.