Russia claimed its airstrikes on Sunday destroyed tanks donated from abroad. There was no immediate confirmation from Ukraine that the Russian airstrikes had destroyed tanks.

Putin's cryptic threat of a military escalation didn't specify what the new targets might be, but it comes days after the United States announced plans to deliver $700 million of security assistance for Ukraine that includes four precision-guided, medium-range rocket systems, helicopters, Javelin anti-tank weapon systems, radars, tactical vehicles, spare parts and more.

Military analysts say Russia is hoping to overrun the embattled eastern Donbas region, where Russia-backed separatists have fought the Ukrainian government for years, before any weapons that might turn the tide arrive. The Pentagon said earlier this week it will take at least three weeks to get the precision US weapons and trained troops onto the battlefield.

Ukraine's nuclear plant operator, Energoatom, said one cruise missile buzzed the Pivdennoukrainsk nuclear plant, about 350 kilometers (220 miles) to the south, on its way to the capital — citing the dangers of such a near miss.

Kyiv hadn't faced any such strikes since the April 28 visit of UN Secretary-General António Guterres. The early morning attack triggered air raid alarms and showed that Russia still had the capability and willingness to hit at Ukraine's heart since abandoning its wider offensive across the country to instead focus its efforts in the east.

In a posting on the Telegram app, the Russian Defence Ministry said high-precision, long-range air-launched missiles were used. It said the strikes destroyed T-72 tanks on the outskirts of Kyiv supplied by Eastern European countries and other armoured vehicles located in buildings of a car-repair business.

In a television interview on Sunday, Putin lashed out at Western deliveries of weapons to Ukraine, saying they aim to prolong the conflict.

"All this fuss around additional deliveries of weapons, in my opinion, has only one goal: To drag out the armed conflict as much as possible," Putin said, alluding to US plans to supply multiple launch rocket systems to Kyiv.

He insisted such supplies were unlikely to change much for the Ukrainian government, which he said was merely making up for losses of rockets of similar range that they already had.

If Kyiv gets longer-range rockets, Putin added, Moscow will "draw appropriate conclusions and use our means of destruction, which we have plenty of, in order to strike at those objects that we haven't yet struck".

The missiles hit Kyiv's Darnytski and Dniprovski districts, Mayor Vitali Klitschko said on the Telegram messaging app, punctuating the Kremlin's recently reduced goal of seizing the entire Donbas.

A billowing pillar of smoke filled the air with an acrid odor in Kyiv's eastern Darnystki district, and the charred, blackened wreckage of a warehouse-type structure was smoldering.

Police near the site told an Associated Press reporter that military authorities had banned the taking of images. Soldiers also blocked off a road in a nearby area leading toward a large railway yard.

The sites struck included facilities for the state rail company, Ukrzaliznytsia, said Serhiy Leshchenko, an adviser in President Volodymyr Zelenskyy's office, on Telegram.

The cruise missiles appeared to have been launched from a Tu-95 bomber flying over the Caspian Sea, the Air Force Command said on Facebook. It said air defense units shot down one missile.

Energoatom said one cruise missile came dangerously close to the Pivdennoukrainsk nuclear power plant.

It said the missile “flew critically low” and that Russian forces "still do not understand that even the smallest fragment of a missile that can hit a working power unit can cause a nuclear catastrophe and radiation leak".

Elsewhere, Russian forces continued their push to take ground in Eastern Ukraine, with missile and airstrikes carried out on cities and villages of the Luhansk region, with the war now past the 100-day mark.

Luhansk governor Serhiy Haidai said on Telegram that "airstrikes by Russian Ka-52 helicopters were carried out in the areas of Girske and Myrna Dolyna, by Su-25 aircraft - on Ustynivka," while Lysychansk was hit by a missile from the Tochka-U complex.

A total of 13 houses were damaged in Girske, and five in Lysychansk. Another airstrike was reported in the eastern city of Kramatorsk by its mayor Oleksandr Goncharenko. No one was killed in the attack, he said, but two of the city's enterprises sustained "significant damage".

On Sunday morning, Ukraine's General Staff accused Russian forces of using phosphorus munitions in the village of Cherkaski Tyshky in the Kharkiv region. The claim couldn't be independently verified.

The update also confirmed strikes on Kyiv, which occurred in the early hours of Sunday. It wasn't immediately clear from the statement which infrastructure facilities in Kyiv were hit.

The General Staff said Russian forces continue assault operations in Sievierodonetsk, one of two key cities left to be captured in the Luhansk region of the Donbas. The Russians control the eastern part of the city, the update said, and are focusing on trying to encircle Ukrainian forces in the area and "blocking off main logistical routes".

The UK military said in its daily intelligence update that Ukrainian counterattacks in Sieverodonetsk were "likely blunting the operational momentum Russian forces previously gained through concentrating combat units and firepower". Russian forces previously had been making a string of advances in the city, but Ukrainian fighters have pushed back in recent days.

The statement also said Russia's military was partly relying on reserve forces of the separatists in the Luhansk region.

The intelligence update said, "These troops are poorly equipped and trained, and lack heavy equipment in comparison to regular Russian units. This approach likely indicates a desire to limit casualties suffered by regular Russian forces."

(With AP inputs)