(Bloomberg) -- President Vladimir Putin demanded that Russia strengthen air defenses around Moscow after the biggest drone attack on the capital since he ordered the invasion of Ukraine, as his Foreign Ministry threatened “the harshest” retaliation against Kyiv.

While the strikes involving eight drones were repelled “satisfactorily” early Tuesday, “it’s clear what needs to be done to seal the air defense in the capital,” Putin said in televised comments during a visit to a creativity center in Moscow. “We will do it.”

The Defense Ministry in Moscow blamed Ukraine for the assault, saying missiles shot down five of the drones while electronic jamming was used to divert three others from their intended targets. Ukraine hasn’t commented formally so far.

UK Foreign Secretary James Cleverly backed Ukraine’s right to strike into Russia in self-defense Tuesday, edging closer to support of such actions than the US or other NATO allies.

“Ukraine does have the legitimate right to defend itself,” Cleverly told reporters in Estonia, while adding that he wasn’t commenting on the most recent attacks. “It has the legitimate right to protect itself within its own borders, of course, but it does also have the right to project force beyond its borders to undermine Russia’s ability to project force into Ukraine itself. So legitimate military targets beyond its own border are part of Ukraine’s self-defense.”

Tuesday’s attack was the most serious incident in Moscow since two drones exploded over the Kremlin on May 3 in an attack that officials also blamed on Ukraine, which denied involvement. Russian territories close to Ukraine have come under fire repeatedly in recent months and the Defense Ministry in Moscow said last week that troops defeated an incursion by attackers who crossed the border into the Belgorod region.

Ukraine carried out the drone attacks on Moscow to try to create panic among residents and those responsible will be “severely punished,” the Russian Foreign Ministry said in a statement on Telegram. 

Several residential buildings were damaged, Moscow Mayor Sergei Sobyanin said. No one was seriously injured although two people sought medical attention and residents of two buildings were evacuated, he said.

‘Sounds of Explosions’

“This morning, residents of some districts of the Moscow region could hear the sounds of explosions — it was our air-defense system working,” Moscow Region Governor Andrey Vorobiev said in his Telegram channel. “Several drones were shot down as they approached Moscow.”

The attack on the capital “cost little but had a fairly high symbolic and psychological-moral impact,” said Pavel Luzin, a Russian military analyst who’s a visiting scholar at the Fletcher School of Law and Diplomacy at Tufts University in Massachusetts. “Its aim is to raise the barrier for what’s acceptable action to counter the Russian aggression.”

The strikes followed another night of Russian attacks on Ukraine’s capital Kyiv, the 17th so far this month. One person was killed and seven were injured, Serhiy Popko, head of Kyiv city’s military administration said on Telegram. 

Air defenses shot down 29 out of 31 Iranian-made drones, mostly directed at Kyiv, Ukrainian officials said. Debris caused fires in several buildings during Russia’s third large-scale attack on the capital in the past 24 hours, according to the city’s military administration. 

How and Why Russia Is Using Iranian Drones in Ukraine: QuickTake

The Kremlin has intensified its bombing campaign ahead of a long-awaited Ukrainian counteroffensive to retake occupied territory in the country’s south and east that Russia seized soon after the February 2022 invasion. Ukraine has accumulated billions of dollars of weapons from its US and European allies for the military assault. 

Russia’s Investigative Committee said it had opened an investigation into the Moscow attacks, the state-run Tass news service reported.

--With assistance from Alex Morales.

(Updates with UK Secretary Cleverly in fourth paragraph)

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