The evacuation of some of the 400,000 residents trapped in a key Ukrainian city has been called off as encircling Russian forces continued to fire in the middle of what was meant to be a ceasefire.

Meanwhile, more evidence is emerging of possible war crimes as footage from the Ukrainian capital reveals a family was murdered in the middle of the street while trying to evacuate.

Ukraine now believes Russia is next planning to bombard the southern port city of Odessa.

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Authorities in the coastal city of Mariupol had said on Sunday night they would make a second attempt to allow residents to leave following days of shelling that has trapped people in without heat, power and water.

But the ceasefire plan collapsed – as it had on Saturday – with each side blaming the other for the failure.

A convoy of evacuees was not able to leave Mariupol because Russian forces continued shelling despite a temporary ceasefire agreement, local authorities said.

“It is extremely dangerous to take people out under such conditions,” the city council said in an online statement.

According to pro-Russian separatists, about 300 people were initially able to leave Mariupol.

Mariupol Mayor Vadym Boichenko said his main priority is to help people escape.

“They’re destroying us,” he told Reuters in a video call during which he could hear the sound of explosions from outside.

He said most residents were sleeping in bomb shelters to escape over six days of near-constant bombardment.

“They’ve been working methodically to make sure the city is blockaded,” Mr Boichenko said.

“They will not even give us an opportunity to count the wounded and the killed because the shelling does not stop.”

For Russia, capture of Mariupol would be a prize – a strategic link between the Russia-backed separatist territories to the north and the land route to the Crimean Peninsula, which Russia annexed in 2014.

Evacuees targeted

Ukrainians have continued to spill into Poland, Romania, Slovakia and elsewhere.

United Nation High Commissioner for Refugees Filippo Grandi said more than 1.5 million people had so far fled in what has been the fastest growing refugee crisis in Europe since World War II.

Families face threat of death – not just from shelling, but from starvation or freezing – by staying in their homes.

Fleeing is also dangerous; Some Russian soldiers clearly have no intention of lowering their weapons to allow for safe evacuations.

Early Monday morning, New York Times photographers published evidence of civilians being killed by Russian forces in a suburb outside Kyiv.

The Times reports that a Russian force advancing on the capital fired mortar shells at a semi-destroyed bridge over the Irpin River.

The bridge was being used by civilians who were fleeing danger with the help of Ukrainian soldiers who reportedly were there to carry bags and children.

“The mortar shells fell first 100 or so yards from the bridge, then shifted in a series of thunderous blasts into a section of street where people were fleeing,” The Times journalists reported from the scene.

“As the mortars got closer to the stream of civilians, people ran, pulling children, trying to find a safe spot. But there was nothing to hide behind.”

A family of four – a mother, father, teenage son and young daughter – were among those hurt.

The woman and children were pronounced dead on the street while the man was unconscious and severely injured.

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“The shelling suggested either targeting of the evacuation routes from Irpin, something of which the Ukrainian authorities have accused the Russian army after a railroad track used for evacuations was hit on Saturday, or disregard for the risk of civilian casualties,” The Times reported.

A huge Russian convoy on a road north of Kyiv has made limited visible progress in recent days, although Russia’s defence ministry released footage on Sunday showing some tracked military vehicles on the move.

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Ukrainian soldiers bolstered defences in the capital by digging trenches, blocking roads and liaising with civil defence units.

“Positions are prepared, we’ve fitted them out and we are simply waiting to meet them here,” said a soldier in a video released by Ukraine’s armed forces.

“Victory will be ours.”

Putin says plan is working

President Vladimir Putin says his campaign in Ukraine is going according to plan and will not end until Kyiv stops fighting.

He made the comments in a phone call with Turkish President Tayyep Erdogan, who appealed for a ceasefire.

Russian media said Mr Putin also held almost two hours of talks on Sunday with French President Emmanuel Macron, who has stayed in regular contact but – as with other international efforts – has yet to convince Russia to call off a campaign now in an 11th day.

Mr Putin told Mr Erdogan he was ready for dialogue with Ukraine and foreign partners but any attempt to draw out negotiation would fail, a Kremlin statement said.

Turkey said Mr Erdogan had called for a ceasefire to ease humanitarian concerns.

Ukraine renewed its appeal to the US and its allies to toughen sanctions beyond existing efforts that have hammered Russia’s economy.

It also requested more weapons, including a plea for Russian-made planes, to help it repel Russian forces.

US Secretary of State Anthony Blinken said his government was “very, very actively” considering how it could backfill aircraft for Poland, if the eastern European country decided to supply its warplanes to Ukraine.

Sanctions have pushed many companies to exit investments in Russia while some Russian banks have been shut out of a global financial payment systems, driving down the rouble and forcing Russia to jack up interest rates.

Tightening the screws further, US payment companies Visa Inc and MasterCard Inc said they would suspend credit card operations in Russia.

-with AAP