Deputy prime minister Yuri Borisov told Russian state television that the Avangard hypersonic glide vehicle flies 27 times faster than the speed of sound, making it impossible to intercept.
He added that the new weapon "essentially makes missile defences useless".
Mr Borisov spoke a day after Russian President Vladimir Putin oversaw the Avangard's reportedly successful test and hailed it as a reliable guarantee of Russia's security for decades to come.
Mr Putin declared that the weapon is impossible to intercept and will ensure the country's security for decades to come.
Speaking to Russia's top military brass after watching the live feed of the launch of the Avangard vehicle from the Defence Ministry's control room, Putin said the successful test was a "great success" and an "excellent New Year's gift to the nation".
The test comes amid bitter tensions in Russia-US relations, which have sunk to their lowest level since Cold War times over the conflict in Ukraine, the war in Syria and the allegations of Russian meddling in the 2016 US presidential election.
Tensions have escalated as the US administration slapped Russia with new waves of sanctions.
The Avangard was among the array of new nuclear weapons that Putin presented in March, saying that Russia had to develop them in response to the development of the US missile defence system that could erode Russia's nuclear deterrent.
In Wednesday's test, the weapon was launched from the Dombarovskiy missile base in the southern Ural Mountains.
The Kremlin said it successfully hit a designated practice target on the Kura shooting range on Kamchatka, 3,700 miles away.
"The Avangard is invulnerable to intercept by any existing and prospective missile defence means of the potential adversary," Putin said after the test, adding that the new weapon will enter service next year with the military's Strategic Missile Forces.
When first presenting the Avangard in March, the Russian leader said the new system has an intercontinental range and can fly in the atmosphere at 20 times the speed of sound, bypassing the enemy's missile defence.
He emphasised that no other country currently has hypersonic weapons.
Putin has said that Avangard is designed using new composite materials to withstand temperatures of up to 2,000c that come from a flight through the atmosphere at hypersonic speeds.
Last week, the Russian leader reaffirmed a strong denial of Washington's claim that Russia had violated the pact, and blamed the US for breaking it.