U.S. President Donald Trump threatened to impose new and severe sanctions on Russia unless it ends its war in Ukraine within 10 days, vowing to take “firm” steps to quickly resolve the conflict.

In Russia’s first response, Deputy Chairman of the Russian Security Council Dmitry Medvedev warned of the dangers of Trump’s statements, considering that “any ultimatum directed at Moscow is a direct step towards war with the United States.”

Medvedev added that those who set tight deadlines for resolving such a complex crisis “should be aware of the consequences of threats to international security.”