Russian and Ukrainian delegations met for talks amid high hopes but low expectations for any diplomatic breakthrough, after Moscow unleashed the biggest land war in Europe since the Second World War but met unexpectedly stiff resistance.

As outgunned but determined Ukrainian forces slowed the Russian advance and sanctions crippled the Russian economy, the military confirmed that its nuclear forces were on high alert, following President Vladimir Putin’s order.

While that raised the unimaginable spectre of nuclear conflict, it was unclear what practical effect it had.

A tense calm reigned on Monday in Kyiv, explosions and gunfire were heard in embattled cities in eastern Ukraine, and terrified Ukrainian families huddled overnight in shelters, basements or corridors.

“I sit and pray for these negotiations to end successfully, so that they reach an agreement to end the slaughter, and so there is no more war,” said Alexandra Mikhailova, weeping as she clutched her cat in a makeshift shelter in the strategic southeastern Ukrainian city of Mariupol.

Around her, parents sought to console children and keep them warm.

Exact death tolls are unclear, but the UN human rights chief said 102 civilians have been killed and hundreds wounded in five days of fighting, warning that figure was likely a vast undercount, and Ukraine’s president said at least 16 children were among the dead.

More than 500,000 people have fled the country since the invasion, another UN official said on Monday, among millions who have left their homes.

Still, a tiny sliver of hope emerged as the first face-to-face talks between Ukrainian and Russian officials since the war began opened on Monday.

The delegations met at a long table with the blue-and-yellow Ukrainian flag on one side and the Russian tricolor on the other.

Ukrainian President Volodymyr Zelensky’s office said it would demand an immediate ceasefire and withdrawal of Russian troops.

But while Ukraine sent its defence minister and other top officials, the Russian delegation was led by Mr Putin’s adviser on culture, an unlikely envoy for ending the war and a sign of how Moscow views the talks.

Meanwhile, Russia’s Central Bank scrambled to shore up the tanking rouble and the US and European countries upped weapons shipments to Ukraine.

While they hope to curb Mr Putin’s aggression, the measures also risked pushing an increasingly cornered Putin closer to the edge and inflicted pain on ordinary Russians.

In Moscow, Russians queued up to withdraw cash as Western sanctions threatened their livelihoods and savings.

In Kyiv, Ukrainians lined up to buy food and water after two nights trapped inside by curfew.

It was not immediately clear what Mr Putin is seeking in the talks, or from the war itself.

Western officials believe Mr Putin wants to overthrow Ukraine’s government and replace it with a regime of his own, reviving Moscow’s Cold War-era influence.

The increasingly erratic Mr Putin made a clear link between ever-tightening sanctions and his decision Sunday to raise Russia’s nuclear posture.

He also pointed at “aggressive statements” by Nato, a reference to his long-held stance that the US-led alliance is an existential threat to Russia.

On Monday, the defence ministry said extra personnel were deployed to Russian nuclear forces, and that the high alert status applies to all their components: the forces that oversee land-based intercontinental ballistic missiles, submarine-launched intercontinental ballistic missiles, and the fleet of nuclear-capable strategic bombers.

It was not immediately clear whether the Kremlin announcement means any nuclear-armed aircraft could already be in the air around Ukraine.

But the move is a clear escalation.

While Russia and the United States typically have land- and submarine-based nuclear forces that are prepared for combat at all times, nuclear-capable bombers and other aircraft are not.

US and British officials played down Mr Putin’s nuclear threat as posturing. But for many, they stirred up memories of the Cuban Missile Crisis and concerns that the West could be drawn into a direct conflict with Russia.

Mr Putin also stepped up his rhetoric, denouncing the US and its allies as an “empire of lies”.

He described Western allies as US “satellites which humbly fawn on it, kowtow to it, copy its conduct and joyfully accept the rules”.

In another possible escalation, neighbouring Belarus could send troops to help Russia as soon as Monday, according to a senior US intelligence official.

US officials say they believe the invasion has been more difficult, and slower, than the Kremlin envisioned, though that could change as Moscow adapts.

Battles also broke out in Ukraine’s second-largest city, Kharkiv, and strategic ports in the country’s south came under assault from Russian forces.

Mariupol, a strategic port city on the Sea of Azov, is “hanging on”, said Zelensky adviser Oleksiy Arestovich.

An oil depot was reportedly bombed in the eastern city of Sumy.

Ukrainian protesters demonstrated against encroaching Russian troops in the port of Berdyansk.

In a war being waged both on the ground and online, cyberattacks hit Ukrainian embassies around the world, and Russian media.

Western nations ramped up the pressure with a freeze on Russia’s hard currency reserves, threatening to bring Russia’s economy to its knees.

Russians withdrew savings and sought to shed roubles for dollars and euros, while Russian businesses scrambled to protect their finances.

The US, European Union and Britain also agreed to block selected Russian banks from the SwiftT system, which facilitates moving money around thousands of banks and other financial institutions worldwide.

In addition to sanctions, the US and Germany announced they will send Stinger missiles to Ukraine among other military supplies.

The European Union, founded to ensure peace on the continent after the Second World War, is supplying lethal aid for the first time, including anti-tank weapons and ammunition.

At least one Western country is studying a request from Ukraine to provide fighter jets, a European official said. She spoke on condition of anonymity to discuss information not yet public.

EU defence ministers were to meet on Monday to discuss how to get the pledged weaponry into Ukraine.

A trainload of Czech equipment arrived on Sunday and another was en route Monday, though blocking off such shipments will clearly be a key Russian priority.

It remains to be seen how much the weaponry will help Ukraine fend off Russia’s vastly greater arsenal.

In New York, the 193-member UN General Assembly scheduled an emergency session Monday on Russia’s invasion.

With the Ukrainian capital besieged, the Russian military offered to allow residents to leave Kyiv via a safe corridor.

The mayor of the city of nearly three million had earlier expressed doubt that civilians could be evacuated.

Ukrainian authorities have been handing out weapons to anyone willing to defend the city.

Ukraine is also releasing prisoners with military experience who want to fight, and training people to make firebombs.

In Mariupol, where Ukrainians were trying to fend off attack, a medical team at a city hospital desperately tried to revive a six-year-old girl in unicorn pyjamas who was mortally wounded in Russian shelling.

During the rescue attempt, a doctor in blue medical scrubs, pumping oxygen into the girl, looked directly into the Associated Press video camera capturing the scene.

“Show this to Putin,” he said angrily.

“The eyes of this child, and crying doctors.”

Their resuscitation efforts failed.

Nearly 560 miles away, Faina Bystritska was under threat in the city of Chernihiv.

“I wish I had never lived to see this,” said Ms Bystritska, an 87-year-old Jewish survivor of the Second World War.