Ukrainians on Wednesday reveled in a surreal display of burnt-out Russian tanks and armor laid out this week as war trophies in central Kyiv to mark the 31st anniversary of independence, but fears of fresh Russian attacks lurked behind their show of defiance.

An air raid siren perforated an eerie calm in Kyiv on the morning of Wednesday's Independence Day following dire warnings that Russia could launch fresh attacks on major cities. Kyiv has warned Moscow of a powerful response if that happens.

The public holiday, which falls six months into Russia's invasion, is usually marked with a military parade, but fearing attacks on mass rallies, Kyiv has banned public events in the city this year and the streets were much quieter than normal.

Authorities in the capital banned large-scale gatherings until Thursday, fearing the national holiday might bring particularly heavy Russian missile attacks.

On Tuesday, the United States also urged its citizens to leave Ukraine if they can, warning of an increased possibility of Russian military strikes on the capital Kyiv in the coming days around Ukrainian independence day as the war reaches the six-month mark.

Ukrainian President Volodymyr Zelenskyy urged the public to be vigilant.

Zelenskyy told Ukrainians in an emotional speech marking 31 years of independence that their country had been "reborn" when Russia invaded and that it would never give up its fight for freedom from Moscow's domination.

In a recorded speech aired on the six-month anniversary of Russia's Feb. 24 invasion, Zelenskyy said Ukraine no longer saw the war ending when the fighting stopped but when Kyiv finally emerged victorious.

"A new nation appeared in the world on Feb. 24 at 4 o'clock in the morning. It was not born, but reborn. A nation that did not cry, scream or take fright. One that did not flee. Did not give up. And did not forget," he said.

The 44-year-old wartime leader delivered the speech in combat fatigues in front of central Kyiv's towering monument to independence from the Russian-dominated Soviet Union that broke up in 1991.

Zelenskyy underscored Ukraine's hardening war stance that opposes any kind of compromise that would allow Moscow to lock in territorial gains, including swathes of southern and eastern Ukraine captured over the past six months.

"We will not sit down at the negotiating table out of fear, with a gun pointed at our heads. For us, the most terrible iron is not missiles, aircraft and tanks but shackles. Not trenches, but fetters," he said.

He vowed that Ukraine would recapture lost territory in the industrial Donbass region in the east as well as the peninsula of Crimea that Russia annexed in 2014.

"What for us is the end of the war? We used to say: peace. Now we say: Victory," he said.

Meanwhile, European leaders pledged unwavering support for Ukraine as the war-torn country marked its Independence Day on Wednesday, coinciding with the six-month milestone of Russia’s invasion.

Leaders paid tribute to the sacrifices and courage of the Ukrainian people, voiced their resolve to keep supplying Ukraine with weapons and reviled Moscow for its attack on the neighboring Eastern European nation.

"I hope (the war) will end this year, so we can be joyful next spring ... I'd like us to get more help, so it can end sooner and we can start living the happy life we had before the war," said Anna Husieva, 27, a Kyiv resident.

In the run-up to the state holiday, citizens had thronged the central thoroughfare, posing for photos by the carcasses of Russian tanks and eating candy floss colored in the yellow and blue of the national flag.

They mused at the irony of the armor display months after Chechen leader Ramzan Kadyrov, an ally of President Vladimir Putin, touted plans for a Russian military parade in Kyiv – until Moscow's assault on the capital was abandoned in March.

"Putin dreamed of a parade on Khreshchatyk, well – here it is," said Pavel Pidreza, 62, a retired Ukrainian soldier who was admiring the tanks on a stroll with his wife, Vira.

Apprehension

Swathes of Ukraine are occupied and there is deep apprehension that the looming winter could be by far the worst since 1991 with natural gas and coal shortages threatening everything from electricity supplies to heating in homes.

Among the revelers in central Kyiv on Monday was a man named Oleksandr, who became lost in tears reflecting on the six months of devastation and exclaimed in a trembling voice that he was unable to speak further.

"Probably no one has done as much to unite Ukraine as Putin," said another resident, Yevhen Palamarchuk, 38. "We always had some internal tensions in the country but since 2014, and especially since February, we are united more than ever."

Independence Day is one of the most important public holidays in Ukraine and has taken on hallowed significance amid what Kyiv says is a Russian imperial-style war of aggression.

Moscow casts the invasion as a special operation to demilitarize a Westward-oriented Ukraine and rid it of people it describes as nationalists, a pretext the West and Kyiv have dismissed as false.

An overwhelming majority of Ukrainians voted in support of independence from the Russia-dominated Soviet Union in a referendum in August 1991.

Palamarchuk said he saw the threat from Russia this week as serious but that Putin did not have many more options for escalating his attack on Ukraine except by resorting to a radical escalation with the use of nuclear weapons.

"At this point, living in Ukraine, there's always the danger of being hit by a rocket. I just don't think statistically it's very likely, that soothes me a little bit," Palamarchuk said.