Possible supplies of US weapons to Ukraine would not only escalate the conflict in its eastern part, but also threaten Russia's security, Russian Foreign Ministry spokesman Alexander Lukashevich said Thursday.

"We are very seriously concerned by these plans. Taking into account the retaliatory plans of Kiev's 'party of war', this could not only escalate the conflict in eastern Ukraine, but also threaten the security of Russia," Tass quoted Lukashevich as saying.

He went on warning that such decision could "significantly damage the Russian-US relations."