Russia threatens escalation after Ukraine hits Moscow with largest-ever drone attack

Russia has pledged to carry out frequent and "massive group strikes" against Ukraine shortly after Kyiv launched a barrage of drones on Moscow, triggering a huge explosion in one of the Russian capital's key oil refineries.

Ukrainian forces conducted a large-scale attack against Moscow on Wednesday evening and Thursday, heavily targeting a major oil refinery located on the south-eastern outskirts of the city.

Nearly 200 drones were reportedly used in the attack, marking Ukraine's biggest-ever air raid on Russia's capital. Authorities said 16 people had been injured, while four Moscow airports temporarily grounded flights.

Columns of black smoke were seen billowing from Gazprom's Moscow Refinery on Thursday, a facility that has been targeted by Ukrainian forces multiple times in recent weeks.

"It is no coincidence that the president announced some time ago, after yet another Kyiv terrorist attack, that we will now conduct massive group strikes on a regular basis against targets whose condition directly affects the combat readiness of the Ukrainian Armed Forces," Russian Foreign Minister Sergei Lavrov told reporters on the sidelines of an event in Kazan on Thursday, according to Interfax.

Ukrainian forces have repeatedly targeted Russia's oil infrastructure, seeking to cut Moscow's energy revenues and try to force President Vladimir Putin into bringing an end to the four-year war.

Ukrainian President Volodymyr Zelenskyy said the strikes on Moscow were in response to attacks from Russia on a historic monastery complex in Kyiv earlier in the week. Russia has said it did not strike the Pechersk Lavra ​monastery.

"This is a fully justified response to Russian attacks on our cities and communities, and another important result of our warriors' work against facilities that sustain Russia's war machine," Zelenskyy said in a social media post on Thursday.

"In recent days, all of our partners have noted the precision and effectiveness of our mid-range strikes and long-range sanctions. It is time the war ended, and Russia must take the necessary steps in diplomacy," he added.

Russian "milbloggers" who closely follow and comment on the war on social media, responded to the strikes on Moscow by raising concern about Russian air defenses and censorship, according to the Institute for the Study of War (ISW), a Washington D.C.-based think tank.

The ISW added that the increasing frequency, size and depth of Ukraine's long-range strike campaign against heavily defended major Russian cities, notably Moscow and St. Petersburg, "demonstrate growing vulnerabilities in Russian air defenses and dilemmas in how the Kremlin chooses to interact with the domestic costs of the war it started."

Russia's Foreign Ministry was not immediately available to comment when contacted by CNBC.

Ukraine's Zelenskyy has been seeking to garner support from both the U.S. and Europe to reach a deal to end the war.

Earlier in the week, U.S. President Donald Trump pledged to provide further assistance to Ukraine and urged the Kremlin to "make a deal" to end the Ukraine war. "I'm going to do whatever I can," Trump told reporters on Tuesday.

The U.S. president added that he had spoken to Zelenskyy and Putin in recent days, saying both countries had "lost tremendous amounts of people."

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