Ukraine on Tuesday launched its biggest ever drone attack on Moscow, killing three people, injuring 18 others and causing a short shutdown at the Russian capital's four airports, Russian officials said.

The dawn attack unfurled as U.S. officials were to meet a Ukrainian delegation in Saudi Arabia to seek an end of the three-year war and as Russian forces try to encircle thousands of Ukrainian soldiers in the western Russian region of Kursk.

Kyiv has suffered repeated mass strikes from Russia throughout the war and said it was targeted by a ballistic missile and 126 drones on Tuesday. It has tried to hit back against its vastly bigger neighbour with repeated drone raids on oil refineries, airfields and even early-warning radar stations.

Moscow Mayor Sergei Sobyanin said Tuesday's was the biggest Ukrainian drone attack on the city, which including the surrounding region has a population of at least 21 million and is one of the biggest metropolitan areas in Europe.

A senior Russian lawmaker suggested Russia should retaliate for Tuesday's raid by striking Ukraine with the Oreshnik hypersonic missile, which Moscow fired on Ukraine last November after the U.S. and U.K. allowed Kyiv to strike deeper into Russia with Western missiles.

Col.-Gen. Andrei Kartapolov, head of parliament's defence committee and a former deputy defence minister, said such a decision was up to President Vladimir Putin. "But I think it would be useful — and not just one," he said.

Miratorg, one of Russia's biggest meat producers, said two employees were killed by falling debris just south of Moscow. A third fatality was later reported in the same area by Evgeniya Khrustaleva, head of the town of Domodedovo.

Another 18 people were injured, including three children, as residences were also struck, Russian officials said.

Commuters carry on

Moscow Region Governor Andrei Vorobyov posted a picture of a wrecked apartment with windows blown out. But there was no sign of panic: commuters went to work as normal.

Russia's aviation watchdog said flights were suspended at all four of Moscow's airports after the attacks, though they were later reopened. Flights were diverted to other cities.

Though U.S. President Donald Trump says he wants to deliver peace in Ukraine, the war is heating up on the battlefield with a major Russian spring offensive in Kursk and a series of Ukrainian drone attacks deep into Russia.

Russia has developed myriad electronic "umbrellas" over Moscow and key installations, with additional advanced internal layers over strategic buildings, and a complex web of air defences to shoot down drones before they reach the Kremlin in the heart of the capital.

The war, the biggest in Europe since the Second World War, has combined grinding trench and artillery warfare with the major innovation of drones.

Moscow and Kyiv have both sought to buy and develop new drones, deploy them in innovative ways, and seek new ways to destroy them - from farmers' shotguns to electronic jamming.

WATCH | Ukrainian soldiers, designers speak about developing more high-tech attack drones:

Ukraine amps up testing of high-tech attack drones as Russian, North Korean troops advance

Ukraine has kept much of its wartime drone program secret. CBC’s foreign correspondent Briar Stewart spoke to Ukrainian soldiers and drone designers about developing more high-tech attack drones. The prospect of possible peace talks pushes both warring sides to try to improve their battlefield positions so they are in a stronger position to negotiate.

Both sides have turned cheap commercial drones into deadly weapons while ramping up their own production.

Soldiers have reported a visceral fear of drones and both sides have used macabre footage of fatal strikes in their propaganda, with soldiers shown being blown apart in toilets or running from burning vehicles.

Putin, who has sought to insulate Moscow from the war, has called Ukrainian attacks on civilian infrastructure such as nuclear power plants "terrorism" and has vowed a response.

Moscow, by far Russia's richest city, has boomed during the war, buoyed by the biggest defence spending splurge since the Cold War.