KYIV, Ukraine, June 6, 2025 (BSS/AFP) - Moscow fired ballistic missiles and attack drones at the Ukrainian capital of Kyiv overnight, killing at least four people after Russian President Vladimir Putin vowed retaliation for an audacious Ukrainian drone attack on Russian airbases.

Deadly attacks have escalated in recent weeks even as the two sides hold talks aimed at finding an end to the three-year war, triggered by Russia's February 2022 invasion.

Tens of thousands have been killed, cities and villages destroyed across eastern Ukraine, and millions forced to flee their homes with Russia's forces controlling around one-fifth of Ukraine's territory.

Russia carried out a barrage of drone and missile strikes across Ukraine overnight on Friday, targeting not only the capital but western regions like Lviv and Volyn, which border EU and NATO member Poland.

At least four people were killed and 20 wounded in the capital, mayor Vitali Klitschko said on social media. AFP journalists heard explosions and air raid sirens echo out over the capital throughout the night.

"Kyiv came under another attack involving UAVs and ballistic missiles. Rescuers are responding to the aftermath at several locations across the city," the State Emergency Service of Ukraine wrote on Telegram.

AFP reporters saw a charred crater in the side of a high-rise residential block in Kyiv, with debris and broken glass strewn across the parking lot in front of the building.

One image published by the head of President Volodymyr Zelensky's office showed a children's playground scattered with rubble and shards of glass.

- Retaliation -

Putin had earlier this week told US President Donald Trump that he would retaliate to a Ukrainian drone attack that damaged nuclear-capable military planes at Russian air bases, including thousands of kilometres behind the front lines in Siberia.

The brazen operation, 18 months in the planning, saw Kyiv smuggle more than 100 small drones into Russia, disguised in a false roof of wood cabins, park them near Russian air bases and then unleash them in a coordinated attack.

The Kremlin said Thursday it would choose "how and when" to respond.

There was no comment from Russian officials Friday on the overnight strikes.

Putin has repeatedly rejected a ceasefire and Russian negotiators have issued a host of sweeping demands on Ukraine if it wants to halt the fighting.

They include completely pulling troops out of four regions claimed by Russia, but which its army does not fully control, an end to Western military support, a ban on Ukraine joining NATO as well as any Western military contingents or hardware being based in the country.

- Rescuers killed -

Multiple fires broke out in various districts of the capital, with the attack also damaging train tracks in the surrounding Kyiv region, leading to lengthy delays, the national railway operator said.

Three of those killed were first responders from the state emergency service, Interior Minister Igor Klymenko said.

"They worked under fire to help people. Another nine rescuers were wounded. Some of them are seriously injured, and doctors are fighting for their lives," he wrote on social media.

Several strikes also hit western Ukraine's city of Lutsk and Ternopil region.

"Today, the enemy carried out the most massive air attack on our region to date. There are multiple strikes," Ternopil's regional military administration chief Vyacheslav Negoda said.

At least 32 people were wounded in four different regions, including 15 in Lutsk, officials said.

Russia said Ukrainian strikes overnight on Russia wounded three people in the western Tula region.

The Russian defence ministry said it downed 174 Ukrainian drones overnight, including 10 headed for the Russian capital, according to Moscow Mayor Sergei Sobyanin said.