Heraldo de Madrid - Ukraine, Russia vow escalation after Moscow attack kills 21 in Kyiv

Ukrainian President Volodymyr Zelensky said his forces would "definitely" retaliate for the overnight pummelling of the capital as he inspected the site of an apartment block partially destroyed in the attack.

In Moscow, the Kremlin vowed to further ramp up the "pressure" on Kyiv, sticking to its no-compromise rhetoric as rescuers in Kyiv scoured the rubble for survivors.

The European Union's top diplomat proposed new sanctions on Moscow, while Zelensky asked the United States for licences to manufacture Patriot air defence missiles.

Russia has routinely launched waves of missiles and drones at Ukrainian cities during its invasion, which has become Europe's deadliest conflict since World War II.

AFP journalists in central and eastern Kyiv heard more than a dozen explosions and saw residents -- some with children and pets -- rushing to shelter in metro stations.

In the morning, locals stood on the rubble of destroyed apartment blocks ripped apart by the barrage, as smoke poured over the Kyiv skyline.

At one spot, a mother cried as she embraced her son in front of the smouldering debris.

Blasts started echoing out late on Wednesday, lasting into the early hours of Thursday as Russian missiles and drones rained down on residential areas in the city centre.

Mayor Vitali Klitschko described it as the "enemy's most massive attack on the capital", without elaborating.

The state emergency services said at least 21 people were killed and 85 were wounded, including two children.

The Ukrainian branch of the Red Cross said that its key warehouse was "destroyed" in the attack with around $2 million worth of humanitarian aid lost.

Debris from the pummelling also damaged a building that was "hosting a number of diplomats", EU spokesperson Anitta Hipper told AFP, adding that "EU diplomats were affected" but "safe".

Kyiv urged its allies to send more air defence.

"Air defence supplies for Ukraine are an absolute and critical priority," Zelensky said in a post on Facebook.

"We also very much count on a decision by the United States regarding licences for Patriots."

Ukraine is seeking to manufacture munitions for the US-made missile interceptor system, one of its only ways of defending against Russian ballistic missiles, although defence experts say it will take time to set up production domestically.

- Struggling to sleep -

Russia fired 496 drones and 74 missiles, including hard-to-intercept ballistic projectiles, Ukraine's air force said.

It said it shot down 48 of the missiles and 476 drones.

AFP reporters met several Kyiv residents outside an apartment building largely destroyed in the attack.

"Half the building has been destroyed. The roof is gone," said 32-year-old factory worker Sabina Mambetova, standing outside the rubble of her home in the eastern Darnytskyi district.

"I've been left without an apartment, alone with my child. I don't know what to do now."

An AFP journalist at the site saw rescuers extracting the body of another victim of the attack, which ripped a multi-storey building open.

Some 52,000 people, including 4,500 children packed into underground stations to shelter from the barrage -- the highest number in recent years, according to the Kyiv metro.

Others hunkered down in basements or corridors through the night as blasts shook buildings across the city.

"It's hard. My child is used to sleeping in complete silence and darkness," 32-year-old doctor Kateryna Kucheryava told AFP from the metro as the attack was unfolding.

"I picked her up and carried her down. She woke up and now she's not sleeping anymore."

Along station platforms, locals set up tents and lay on air mattresses and camping chairs, while mothers tried to sleep clutching babies to their chests.

- Zelensky cuts short visit -

The EU's top diplomat Kaja Kallas said she would propose new sanctions on Moscow over the attack.

But the Kremlin showed no signs it would back down, more than four years into an invasion that has killed hundreds of thousands.

The attack came hours after Zelensky cut short a visit to Dublin on Wednesday, citing intelligence reports of an impending Russian strike.

Zelensky said Russian President Vladimir Putin "has been preparing this massive strike against Ukraine for some time now".

Russian officials have reported repeated strikes in border regions, while Moscow has said its air defences have intercepted hundreds of drones from Ukraine in recent days.

US efforts to broker an end to the conflict have so far failed.

E.Nieto--HdM