A 28-year-old U.S. citizen was detained at Moscow’s Vnukovo airport after Russian authorities allegedly found food items containing cannabis derivatives in his luggage. The man had arrived from Istanbul on Feb. 7 when a customs inspection led to his arrest, according to Russian state-run news agencies TASS and Interfax.

Russia’s Federal Customs Service claimed that a service dog alerted officials to one of the man’s suitcases, prompting a search. Inside, authorities reportedly discovered two plastic jars and a zip bag containing sweets. A chemical analysis later confirmed that the items contained narcotic substances from the cannabinoid group, TASS reported.

The detained traveler reportedly told officials that the gummies and marmalade had been prescribed to him by a doctor in the United States. He claimed he needed the products while traveling, according to TASS. The possession of cannabis, even for medical use, is illegal in Russia.

The U.S. State Department has not yet commented on the case. The detention comes amid ongoing tensions between the U.S. and Russia, including previous high-profile detentions of American citizens.

Earlier this week, Russia and the U.S. carried out a prisoner exchange, with Moscow releasing U.S. teacher Marc Fogel in exchange for Alexander Vinnik, a Russian national accused of Bitcoin fraud. Fogel had been sentenced to 14 years in prison for carrying marijuana he claimed was medically prescribed.