MOSCOW (Reuters) - Russia may respond to any U.S. confiscation of its currency reserves frozen in the West by seizing the assets, including property and cash, of U.S. citizens and investors in Russia, Dmitry Medvedev, a senior security official, said on Saturday.

The U.S. House of Representatives has passed a bill allowing the Biden administration to confiscate Russian assets held in American banks and transfer them to Ukraine, something the Kremlin has said would be illegal and trigger retaliation.

In response to Russia's war in Ukraine, the United States and its allies prohibited transactions with Russia's central bank and finance ministry and blocked about $300 billion of sovereign Russian assets in the West, most of which are in European not American financial institutions.

The Group of Seven (G7) major democracies is also looking at what it may be able to do around the frozen Russian assets.

Medvedev, a close ally of President Vladimir Putin and the deputy chairman of Russia's Security Council, said on Saturday that Russia would not be able to retaliate in kind against any U.S. seizure of its reserves.

"The reason is clear - we do not have a significant amount of American state property, including money, rights and other US assets. Therefore, the answer can only be asymmetrical. It is not a fact that it will be any less painful," Medvedev wrote on his official Telegram channel.

"We are talking about the foreclosure, for example by a court decision, on the property of private individuals located in the jurisdiction of Russia (money, real estate and movable property in kind, property rights)."

"Yes, this is a complex story, since these individuals usually acted as investors in the Russian economy," Medvedev said. "And we guaranteed them the inviolability of their private property rights. But the unexpected happened - their state declared a hybrid war on us. This must be answered."

He said the law in Russia would need to be changed to allow such asset seizures in favour of the Russian state.

Russian Central Bank governor Elvira Nabiullina said on Friday Moscow would defend its legitimate interests in the event that its assets were confiscated, but did not disclose the strategy and tactics.