Ukraine's massive drone swarm attack on the Russian capital, targeting critical energy infrastructure including a major refinery and storage tank farms, has sparked fuel-shortage fears in Moscow while prompting Russia to warn Kyiv of "massive group strikes" in retaliation.

On Thursday, 200 Ukrainian suicide drones swarmed Gazprom's Moscow Refinery in what military observers are calling Kyiv's most brazen offensive of the four-year war to date.

Footage from the southeastern outskirts of the city showed the drone swarm attack and the resulting columns of black smoke billowing from the heavily damaged refinery and storage tank farms.

"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 yesterday, according to Interfax.

Ukraine's drone attack appears to have targeted Russia's refining capacity, as concerns grow that fuel shortages could soon materialize in the capital area.

Sergey Vakulenko, a senior fellow at the Carnegie Russia and Eurasia Center in Berlin and a former Russian oil executive, told Bloomberg that a gas shortage in Moscow is now unavoidable.

"The authorities will do everything they can to bring fuel in from other regions," Vakulenko said. "However, rail capacity is not unlimited, and nearby refineries have also been damaged."

Kyiv has been pounding away at Russia's energy infrastructure with drones. The latest data from EA Analytics indicates that Russian crude-processing rates are set to drop to two-decade lows in June.

Here's TD Securities Roman Schweizer's first take on the attack:

What Russia's "massive group strikes" response will look like remains to be seen, but the threat of gray-zone sabotage across the West is rising. That could include a campaign of cyberattacks, arson, logistics disruption, rail and port interference, telecom or undersea-cable incidents, and attacks against defense supply-chain nodes supporting Ukraine.