"Forcefully reject unacceptable and unfounded allegation by Russian MFA spokesperson that nerve agent used in Salisbury might originate in Sweden. Russia should answer UK questions instead," Wallstrom said on Twitter.
Earlier, Russian Foreign Ministry spokeswoman Maria Zakharova said that the most likely sources of origin of the Novichok substance were the United Kingdom, Slovakia, the Czech Republic, Sweden and, possibly, the United States.
On Wednesday, May went on to announce a package of anti-Russian measures, including the expulsion of 23 Russian diplomats from the country, and the suspension of bilateral contacts between London and Moscow.
Russia categorically refutes its involvement in the poisoning of the Skripals.