Russia will unleash "the next wave of hell" on besieged Ukrainian city Mariupol after it refused to surrender - but lacks the firepower to escalate its assault, experts believe.
The city has been "comprehensively trashed" by missiles fired by Vladimir Putin's forces, but defiant leaders today said there was "no question" they would lay down their arms.
Civilian buildings including a theatre where families were hiding have been targeted in recent days, while President Volodymyr Zelenskiy, said the siege was "a terror that will be remembered for centuries to come".
Tens of thousands remain trapped inside Mariupol, a port on the Azov Sea, as Ukrainian troops and volunteers bravely defend their homeland against the advancing invaders.
Russia is determined to seize the city and Putin's forces have completely encircled it on both land and sea, stopping vital supplies getting in and out.
Professor Mark Galeotti, principal director of Mayak Intelligence, said that Russia would never have expected Ukraine to surrender the city, and the surrender call was little more than posturing.
He told The Mirror: "As much as anything else it was grandstanding so they can say 'look, we're being reasonable' before they unleash the next wave of hell."
Prof Galeotti said Mariupol has been "comprehensively trashed" by the bombardment, but civilian casualties will continue to rise in coming days.
"In the grand scheme of things the Russians aren't in a position to escalate, but the point is that they've chosen Mariupol as a key target," he said.
"Mariupol has become a symbolic site of resistance and one way or another they will make sure that they take it."
He continued: "For Putin every extra city he can take is an extra bargaining chip."
He said that with the city completely cut off, every Ukrainian troop killed would be one less enemy to fight, as reinforcements are unable to reach Mariupol.
On Friday Russian forces unleashed high-tech hypersonic missiles for the first time in combat - a move Prof Galeotti said could indicate it is running out of conventional weaponry.
"It's like using a Rolls Royce to go and do a weekly shop," he said. "It's a ridiculously expensive missile that they've used for a purpose that it didn't deserve, but they're looking at what else they've got in the cupboard.
"It's an area in which the Russians have a technical advantage, it's possible that they're saying 'don't mess with us.'"
Prof Galeotti said seizing Mariupol would not be a "war winning" moment for the Russians, but it would be a heavy blow for Ukraine.
"Now we're getting reports of Russians in Mariupol, it implies that we're approaching the end game."
Mariupol has been bombarded with missiles in the three weeks since the war began, but this now means Russian forces are running out of targets in the city, Dr Deborah Sanders told The Mirror.
Even Kremlin supporters believe that taking Mariupol will not be easy, despite the merciless bombing.
Dr Sanders, reader in Defence and Security Studies at King's College London, told The Mirror that the refusal to surrender would likely lead to a "continuation" of the assault on the city, but not necessarily an increase.
She said she believes Russia lacks the firepower to intensify the attack, and Ukraine cannot afford to give up any territory.
Dr Sanders said: "They (Russia) do not have the firepower to necessarily be able to intensify the attack as they are heavily engaged in the other theatres with a continued push on Odesa.
"Taking Kyiv or at least regime change - overthrowing President Zelensky - remains they key priority.
"One problem they are likely to face is what targets to hit, very little remains standing in Mariupol. If President Putin's aim is to coerce the Ukrainians into accepting his peace terms, then he is lacking a ladder of escalation.
"Not only is there a lack of military capacity to intensify shelling, but a continuation of this tactic will make increased sanctions more likely."
Mariupol is of such importance to Ukraine that it "will never willingly surrender" it, Dr Sanders said.
She stated: "The Ukrainians need to demonstrate that they can take the pain, that they will continue to fight, this will put them in a much stronger negotiating position.
"In essence, the Ukrainians need to drag this war out as long as possible, as the costs to Russia are immense - both in terms of the military costs, but also in terms of the reputational and economic costs of sanctions.
"The costs to Ukraine, of course, are also immense, but they could be much much worse and Ukraine could end up losing large swathes of its territory in the east, access to the Sea of Azov and its very independence."
A Russian-backed separatist leader in eastern Ukraine said he believed it would take more than a week to take control of the besieged Ukrainian port city of Mariupol.
Denis Pushilin, head of the so-called Donetsk People's Republic, told Russia's Interfax news agency: "I am not so optimistic that two or three days or even a week will close the issue. Unfortunately, no, the city is big."
It comes after a deadline for Ukrainian leaders to surrender the city passed in the early hours of this morning.
Russian Colonel-General Mikhail Mizintsev, head of the Russian National Defence Control Centre, urged Ukrainian forces in Mariupol: “Lay down your arms.
“A terrible humanitarian catastrophe has developed. All who lay down their arms are guaranteed safe passage out of Mariupol.”
"There can be no question of any surrender, laying down of arms," the Ukrainska Pravda news portal cited Ukraine's Deputy Prime Minister Iryna Vereshchuk as saying early on Monday.
"We have already informed the Russian side about this."
Mrs Vereshchuk said over 7,000 people were evacuated from Ukrainian cities through humanitarian corridors on Sunday, with more than half escaping from Mariupol.
