In April 2021, Zeman cast doubt on Russia's involvement in the 2014 Vrbětice ammunition warehouses explosions, suggesting that the deadly blast could have been caused accidentally due to the mishandling of explosives, and that there was no conclusive evidence to accuse Russia. In response, thousands of demonstrators took to the streets in Prague on 29 April 2021, calling Zeman "a servant" of Russia, and demanding he be tried for treason.