MOSCOW — Moscow may respond to Western sanctions by opting out of the last nuclear arms deal with the U.S., cutting diplomatic ties with Western nations and freezing their assets, a senior Russian official warned Saturday as Russia’s ties with the West dived to new lows over its invasion of Ukraine.

Dmitry Medvedev, the deputy head of Russia’s Security Council chaired by President Vladimir Putin, also warned that Moscow could restore the death penalty after it was removed from Europe’s top rights group.

The sanctions placed new tight restrictions on Russian financial operations, imposed a draconian ban on technology exports to Russia and froze the assets of Putin and his foreign minister, a harsh response that dwarfed earlier Western restrictions. Washington and its allies say that even tougher sanctions are possible, including kicking Russia out of SWIFT, the dominant system for global financial transactions.

In sarcastic comments posted on a Russian social platform, Medvedev dismissed the sanctions as a show of Western “political impotence” that will only consolidate the Russian leadership and foment anti-Western feelings.

“We are being driven out of everywhere, punished and threatened, but we don’t feel scared,” he said, mocking the sanctions imposed by the U.S. and its allies as an attempt to vindicate their past “shameful decisions, like a cowardly retreat from Afghanistan.”

Medvedev was placeholder president in 2008-2012 when Putin had to shift into the prime minister’s seat because of term limits. He then let Putin reclaim the presidency and served as his prime minister for eight years.

During his tenure as president, Medvedev was widely seen as more liberal compared with Putin, but on Saturday he made a series of threats that even the most hawkish Kremlin figures haven’t mentioned to date.

Medvedev noted that the sanctions offer the Kremlin a pretext to completely review its ties with the West, suggesting that Russia could opt out of the New START nuclear arms control treaty that limits the U.S. and Russian nuclear arsenals.

The treaty, which Medvedev signed in 2010 with then-U.S. President Barack Obama, limits each country to no more than 1,550 deployed nuclear warheads and 700 deployed missiles and bombers, and envisages sweeping on-site inspections to verify compliance. The pact, the last remaining U.S.-Russian nuclear arms control agreement, had been set to expire in February 2021 but Moscow and Washington extended it for another five years.

If Russia opts out of the agreement now, it will remove any checks on U.S. and Russian nuclear forces and raise new threats to global security.

Medvedev also raised the prospect of cutting diplomatic ties with Western countries, charging that “there is no particular need in maintaining diplomatic relations” and adding that “we may look at each other in binoculars and gunsights.”

Referring to Western threats to freeze the assets of Russian companies and individuals, Medvedev warned that Moscow wouldn’t hesitate to do the same.

“We would need to respond in kind by freezing the assets of foreigners and foreign companies in Russia … and possibly by nationalizing the assets of those who come from unfriendly jurisdictions,” he said. “The most interesting things are only starting now.”

Commenting on the Council of Europe’s move Friday to suspend Russia’s representation in Europe’s leading human rights organization, Medvedev contemptuously described it as one of “useless nursing homes” that Russia mistakenly joined.

He added that it offers “a good opportunity” to restore the death penalty for grave crimes, noting that the United States and China have never stopped using it.

Moscow has maintained a moratorium on capital punishment as part of its obligations since it joined the Council of Europe in 1996, and Medvedev’s statement shocked the nation’s rights defenders and activists.