Photographs of the distinctive air defense system were published on social media.

More air defense systems were installed at several other sites in or near Moscow, including Odintsovo district, about six miles from President Vladimir Putin’s residence at Novo-Ogaryovo outside the capital, according to the Russian media outlet Sirena, which posted video and still images.

Russian military analyst Ruslan Leviev of Conflict Intelligence Team, an independent group that analyzes open source intelligence, reported that an S-400 air defense system would be installed in the Losiny Island Park outside Moscow, where trees have been cleared in recent days. Leviev spoke on Popular Politics, a YouTube channel associated with jailed opposition leader Alexei Navalny.

Asked Friday whether the Kremlin feared airstrikes could be carried out against Moscow, Putin spokesman Dmitry Peskov referred queries to the Russian Ministry of Defense. “They are responsible for ensuring the security of the country in general and the capital in particular, so it’s better to ask the Ministry of Defense about all the measures that are being taken,” Peskov said.

The Russian Defense Ministry rarely responds to questions from Western media and did not reply to an emailed question Friday. The range of the Pantsir-S1 defense system would cover much of central Moscow, including the Kremlin.

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The positioning of the weapons follows criticism from Russian analysts about gaps in Russia’s air defenses after at least four Ukrainian strikes last month on military airfields deep inside Russia, three of them targeting the Engels military air base near Saratov, where Russia bases long-range strategic bombers. Another struck the Diagilevo air base near Ryazan, about 114 miles southeast of Moscow.

“It looks like they are drawing conclusions from the fact that Ukrainian drones were flying into bases far in the rear, such as those in Diagilevo and Engels,” Leviev said. “Apparently because of this fear, and in general because of Vladimir Putin’s fear of missile attacks, they decided to strengthen Moscow’s defenses in this way, because they understand very well that with such a leaky Russian air defense along the border, apparently Ukrainian drones can theoretically reach Moscow as well.”

The December attacks demonstrated Kyiv’s ability to strike deep in Russian territory as Ukraine continues to struggle to regain territory lost during Moscow’s full-scale invasion.

The airstrikes in Russia followed a string of other Ukrainian surprise attacks that have humiliated Moscow, including the bombing of a bridge linking Crimea to Russia, strikes on Saki air base in Crimea, and the sinking of the warship Moskva, the flagship of Russia’s Black Sea Fleet.

Russia is reinforcing its capital’s defenses as Putin has been preparing the Russian public for a long, difficult war against Ukraine and a prolonged confrontation with NATO.

Putin has shifted Russia’s economy to a wartime footing, demanding that companies serve the war effort, and has increasingly militarized Russian society, intensifying a propaganda effort to buttress support for the war, amid rising casualties at the front and swirling rumors of a possible second, unpopular mass mobilization.

Since the start of the invasion, Putin has crushed his political opposition and Russia has squashed resistance to the war by banning protests, curbing free speech and imprisoning critics.

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On Tuesday, Putin ordered an increase of more than 350,000 personnel in Russia’s military strength — to a total of 1.5 million, although it is far from clear that the country can muster enough volunteer contract soldiers to reach that target.

After winter slowed their advances, Russian and Ukrainian forces are each reported to be preparing new offensives, setting the stage for what could be a decisive phase in the war in coming months.

The sight of air defense missiles in central Moscow is another sign of the war being normalized in Russian life.

As the invasion drags on, officials, including Putin, increasingly refer to it as a “war” being waged by NATO against Russia, characterizing it, without evidence, as an existential battle for survival against greedy Western powers determined to dismember and gobble up the Russian nation.

After the strikes in early December on two Russian air bases, Russian military historian Yuri Knutov, the director of the Museum of Air Defense Forces, told state television that Russia left holes in its air defense system when it sent much of its military equipment to Ukraine.

“Gaps formed in our air defense system. American satellites can see these gaps well. I don’t doubt it, and the specialists do not doubt it,” Knutov warned at the time.

The prominent Russian pro-war military blogger Alexander Kots, a journalist with the mass-circulation pro-Kremlin tabloid Komsomolskaya Pravda, wrote on his Telegram channel that the installation of air defense systems in the capital was a positive sign, demonstrating that Russian authorities “understand that strikes against Moscow and the region are a matter of time.”

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Leviev said the newly installed air defense systems were a last resort, in case a missile or drone managed to evade outer Russian air defenses to reach Moscow. If not for the war, he added, such systems would be positioned far from Moscow, “but Russia is a belligerent country now, and drones are coming into Russia, so this is pretty much expected.”

As Western officials weighed sending heavy battle tanks to Ukraine, the deputy chairman of the Russian Security Council, Dmitry Medvedev, warned on Thursday that nuclear powers such as Russia could not lose wars, and he threatened that Western efforts to support Kyiv could trigger a nuclear war. It was the latest of a number of nuclear threats issued by senior Russian officials.