A 28-year-old American has been detained in Russia after customs officials allegedly found cannabis-laced marmalade in his luggage, Russian media reported Friday.

K. Byers, a US citizen, was arrested at Moscow’s Vnukovo airport after arriving from Istanbul last Friday. Authorities accuse him of attempting to smuggle a “significant amount” of drugs into the country, which carries a potential sentence of up to seven years in prison.

The U.S. State Department has not yet commented on the arrest. The detention follows the recent Washington-Moscow prisoner exchange, in which Russia returned American teacher Marc Fogel, who had been jailed for medically prescribed marijuana, in exchange for Russian cryptocurrency expert Alexander Vinnik. The White House had hailed the swap as a diplomatic breakthrough and a step toward possible peace talks between Russia and Ukraine.

The arrest of Byers risks straining relations between the two countries just after Trump said there was a “good possibility” of ending the war after he spoke to Russian President Vladimir Putin on the phone on Wednesday.