If profitable, the Russian offensive in what is named the Donbas would primarily slice Ukraine in two.
It will give Russian President Vladimir Putin a badly wanted victory after the failed try by Moscow's forces to storm the capital, Kyiv, and heavier-than-expected casualties almost two months into the warfare.
The cities of Kharkiv and Kramatorsk got here below lethal assault, and Russia additionally mentioned it struck areas round Zaporizhzhia and Dnipro west of the Donbas with missiles.
Russian Defence Ministry spokesman Main Common Igor Konashenkov mentioned air-launched missiles destroyed 13 Ukrainian troop and weapons places, whereas the air drive struck 60 different Ukrainian navy services, together with missile warhead storage depots.
Russian artillery hit almost 1300 Ukrainian navy services and greater than 1200 troop concentrations over the previous 24 hours, he mentioned. The claims couldn't be independently verified.
In what each side described as a brand new part of the warfare, the Russian assault started on Monday alongside a entrance stretching greater than 480km from north-eastern Ukraine to the nation's southeast.
Ukraine's navy mentioned Russian forces tried to "break by means of our defences alongside almost all the entrance line."
Weeks in the past, after the abortive Russian push to take Kyiv, the Kremlin declared its foremost purpose was the seize of the principally Russian-speaking Donbas, the place Moscow-backed separatists have been combating Ukrainian forces for eight years.
A Russian victory within the Donbas would deprive Ukraine of the economic belongings concentrated there, together with mines, metals vegetation and heavy-equipment factories.
A senior US defence official, talking on situation of anonymity to debate the Pentagon's assessments of the warfare, mentioned the Russians had added two extra fight models, often known as battalion tactical teams, in Ukraine over the previous 24 hours.
That introduced the full variety of models within the nation to 78, all of them the south and the east, up from 65 final week, the official mentioned.
That may translate to about 55,000 to 62,000 troops, based mostly on what the Pentagon mentioned at the beginning of the warfare was the everyday unit energy of 700 to 800 troopers. However precisely figuring out Russia's combating capability at this stage is troublesome.
A European official, likewise talking on situation of anonymity to debate navy assessments, mentioned Russia additionally has 10,000 to twenty,000 overseas fighters within the Donbas.
They're a mixture of mercenaries from Russia's personal Wagner Group and Russian proxy fighters from Syria and Libya, in response to the official.
Whereas Ukraine portrayed the assaults on Monday as the beginning of the long-feared offensive within the east, some observers famous that an escalation has been underway there for a while and questioned whether or not this was really the beginning of a brand new offensive.
The US official mentioned that the offensive within the Donbas has begun in a restricted method, primarily in an space south-west of the town of Donetsk and south of Izyum.
Justin Crump, a former British tank commander now with the strategic advisory firm Sibylline, mentioned the Ukrainian feedback may, partly, be an try to influence allies to ship extra weapons.
"What they're attempting to do by positioning this, I feel, is ... focus individuals's minds and energy by saying, 'look, the battle has begun within the Donbas,'" Mr Crump mentioned.
"That partly places strain on NATO and EU suppliers to say, 'guys, we're beginning to battle now. We want this now.'"
European and American arms have performed a key function in enabling the outgunned Ukrainians to carry off the Russians.
The Dutch Prime Minister instructed Ukrainian President Volodymyr Zelenskyy on Tuesday that the Netherlands would ship "heavier materials," together with armoured automobiles.
Related Press journalists in Kharkiv mentioned a minimum of 4 individuals have been killed and three wounded in a Russian assault on a residential space of the town. The assault occurred as residents tried to keep up a way of normalcy, with municipal employees planting spring flowers in public areas.
An explosion additionally rocked Kramatorsk, killing a minimum of one particular person and wounding three, in response to AP journalists on the scene.
Eyewitness accounts and experiences from officers have given a broad image of the extent of the Russian advance. However impartial reporting within the elements of the Donbas held by Russian forces and separatists is severely restricted, making it troublesome to know what is going on in lots of locations on the bottom.
Navy consultants mentioned the Russians' purpose is to encircle Ukrainian troops from the north, south and east.
Key to the marketing campaign is the seize of Mariupol, the now-devastated metropolis within the Donbas that the Russians have besieged for the reason that early days of the warfare.
Taking Mariupol would deprive Ukraine of a significant port and full a land bridge between Russia and the Crimean Peninsula, seized from Ukraine from 2014.
It will additionally release Russian troops to maneuver elsewhere within the Donbas.
A number of thousand Ukrainian troops, by the Russians' estimate, remained holed up in a sprawling Mariupol metal plant, representing what was believed to be the final main pocket of resistance within the metropolis.
On Tuesday, Russia issued a brand new ultimatum to the Ukrainian defenders to give up, saying those that come out will "preserve their lives," and mentioned a cease-fire was being declared within the space so the combatants may go away the plant.
The Ukrainians have ignored earlier such affords, and there was no rapid affirmation a cease-fire occurred.
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The Kremlin-backed chief of Chechnya, Ramzan Kadyrov, whose forces have taken half within the combating in Mariupol, mentioned on a messaging app that Russian forces would root out the Ukrainian resistance inside hours and take full management of the metal mill on Tuesday.
Mr Kadyrov is thought for his bluster and has repeatedly predicted the town's fall up to now.