Discussions about allowing Ukraine to use the Patriot air defence system over Russian territory show the West is on a path of escalation, the TASS news agency cited Russia's foreign ministry as saying on Monday.
Russia will take all measures to thwart such threats, the ministry said.
Russia's foreign ministry warned the United States against "mistakes that may have fatal consequences" with regards to allowing Ukraine to strike targets on Russian soil.
Deputy Foreign Minister Sergei Ryabkov said attempts by Kyiv to attack Russian early-warning radar systems would be thwarted and Moscow may respond asymmetrically to such steps.
