By DAVID KEYTON and YESICA FISCH
KYIV, Ukraine (AP) -- Russia shifted a dozen crack units from the shattered port of Mariupol to eastern Ukraine and pounded away at cities across the region, Ukrainian authorities said Friday, as the two sides hurtled toward what could be an epic battle for control of the country's industrial heartland.
Russian state TV showed the Russian flag raised on what it said was Mariupol's highest point, the city's TV tower. It also showed what it said was the tallest building at Mariupol's besieged Azovstal steel plant in flames.
The Kremlin has thrown over 100,000 troops and mercenaries from Syria and Libya into the fighting in Ukraine and is deploying more forces in the country every day, said Oleksiy Danilov, secretary of Ukraine's National Security and Defense Council.
"We have a difficult situation, but our army is defending our state," he said.
Cities came under bombardment in the Donbas -- the industrial region in the east that the Kremlin has declared the new, main theater of war -- as well as in the Kharkiv region just to the west, and in the south, authorities said.
Russian forces pummeled an estimated 2,000 Ukrainian fighters holed up inside the sprawling Azovstal plant, the last known pocket of resistance inside the strategic southern port city, the mayor's office reported.
"Every day they drop several bombs on Azovstal," said Petro Andryushchenko, an adviser to Mariupol's mayor. "Fighting, shelling, bombing do not stop."
Just a day earlier, Russian President Vladimir Putin declared victory in the battle for Mariupol despite the steel-mill holdouts. He ordered his forces not to storm the plant to finish off the defenders but to seal it off instead in an apparent bid to force them to surrender.
Mariupol has taken on outsize importance in the war. Capturing it would deprive the Ukrainians of a vital port and complete a land corridor between Russia and the Crimean Peninsula, which seized from Ukraine in 2014.
It would also enable Putin to throw more of his forces into the potentially climactic battle for the Donbas and its coal mines, factories and other industries, or what the Kremlin has now declared to be its main objective.
Danilov reported that some 12 to 14 of Russia's elite military units have, in fact, left Mariupol and begun moving to the east to take part in the fighting there.
"It will now be difficult for our forces, because our guys in Mariupol were taking (those units) on themselves. It is their courage and feat," he said.
Danilov also said Kyiv was able to deliver weapons via helicopter at great risk under cover of night to the Mariupol steelworks, which have been bombarded for weeks.
Putin said Russia gave Ukrainian forces inside the plant the option to surrender, with guarantees to keep them alive, and offered "decent treatment and medical care," according to an account of a phone call with European Council President Charles Michel, provided by the Kremlin.
"But the Kyiv regime does not allow them to take this opportunity," Putin charged.
More than 100,000 people -- down from a prewar population of about 430,000 -- are believed trapped in the city with little food, water or heat, and over 20,000 civilians have been killed in the nearly two-month siege, according to Ukrainian authorities.
Repeated attempts to evacuate civilians from the city have failed because of what the Ukrainians said was continued Russian shelling.
Ukrainian Deputy Prime Minister Iryna Vereshchuk said no humanitarian corridors for civilian evacuations would be open in Ukraine on Friday because it was too dangerous. She urged civilians to "be patient" and "hang in there."
Days into the Russian offensive to take the east, the campaign has yet to become a full-out assault, with military analysts saying Moscow's forces are still ramping up and have yet to achieve any major breakthroughs in the Donbas or gain any significant ground.
But scattered towns in the east have experienced the thud of incoming shells that drive citizens out in panic.
Slovyansk, a city of about 100,000 in eastern Ukraine, came under fire during the night, according to the mayor, who said no injuries were reported but urged residents to leave via bus convoy. In Rubizhne, Russian fire prevented attempts to bring buses in, the regional governor said.
Intensive shelling was also heard overnight in Kharkiv, a northeastern city that lies outside the Donbas but is seen as one of the gateways the Russians intend to use to encircle Ukrainian forces in the Donbas from the north, south and east.
In other developments, Russian Foreign Minister Sergey Lavrov said talks between the two countries have "ground to a halt" because Moscow hasn't received a response from Kyiv to its latest proposals, the details of which have not been released.
Putin's lead negotiator at the talks, Vladimir Medinsky, said he held several lengthy conversations Friday with the head of the Ukrainian delegation. He gave no further details.
Also, Rustam Minnekayev, a senior Russian military official, publicly outlined Russian war aims that appeared to be wider than what the Kremlin has stated in recent weeks. He said Russia's forces aim to take full control of not just eastern Ukraine but southern too.
He said such a move would open the way to the nation of Moldova, where Russia backs the breakaway region of Transnistria. Moldovan officials are warily watching Putin's actions in Ukraine.
On Thursday, satellite photos from Maxar Technologies revealed what appeared to be rows upon rows of more than 200 freshly dug mass graves on the outskirts of Mariupol, prompting accusations that the Russians are trying to conceal the slaughter of civilians taking place in the city.
Initial estimates from the Ukrainians said the graves could hold 9,000 bodies.
There was no immediate reaction from the Kremlin on the satellite pictures.
The U.N. Human Rights office again condemned the Russian invasion.
"Over these eight weeks, international humanitarian law has not merely been ignored but seemingly tossed aside," U.N. High Commissioner for Human Rights Michelle Bachelet said.