By Natalia Zinets and Emma Farge

KYIV (Reuters) -Civilians including women and children will need to be dug from bunkers under a steel works that is the last holdout of resistance in Ukraine's Mariupol, President Volodymyr Zelenskiy said on Thursday, as Russian forces pressed their assault.

After failing to capture the capital Kyiv in the early weeks of a war that has killed thousands and flattened cities, towns and villages, Russia has accelerated its attacks across southern and eastern Ukraine.

Russia's military said it would pause military activity at the Azovstal steel works in the port city of Mariupol during Thursday daytime and the following two days to allow civilians to leave.

In an early morning address, Zelenskiy said Ukraine stood ready to ensure a ceasefire in Mariupol.

"It will take time simply to lift people out of those basements, out of those underground shelters. In the present conditions, we cannot use heavy equipment to clear the rubble away. It all has to be done by hand," Zelenskiy said.

Ukrainian fighters inside Azovstal are fighting "difficult, bloody battles" against Russian troops, Denis Prokopenko, a commander with Ukraine's Azov regiment, said late on Wednesday.

Ukraine's military general staff said Russia's assault on the sprawling Soviet-era plant included air support.

Moscow declared victory in Mariupol on April 21 after weeks of siege and shelling, but resistance by Ukrainian forces in Azovstal has prevented Russia completely overrunning the city.

Mariupol is a major target in Russia's efforts to cut Ukraine off from the Black Sea - vital for its grain and metals exports - and link Russian-controlled territory in the east of the country to Crimea, seized by Moscow in 2014.

EVACUATIONS

The United Nations and Red Cross evacuated hundreds of people from Mariupol and other areas this week. But an estimated 200 civilians, as well as Ukrainian fighters, are still holed up in a network of underground bunkers at Azovstal, Ukrainian officials say.

Over 300 civilians were evacuated on Wednesday from Mariupol and other areas in southern Ukraine as part of a joint U.N.-Red Cross operation, U.N. humanitarian coordinator for Ukraine Osnat Lubrani said.

But nobody from Azovstal was among the group, said Jens Laerke, spokesperson for the U.N. humanitarian office.

"We fear more civilians are trapped there, though, and stand ready to help," Laerke said in an email.

Tetyana Trotsak, an Azovstal evacuee among dozens who reached a Ukraine-controlled town this week, voiced fear for those still trapped inside the steel plant.

"God forbid more shells hit near the bunkers where the civilians are," Trotsak said.

BATTLES

Elsewhere, Pavlo Kyrylenko, governor of the eastern Donetsk region in which Mariupol is located, said at least 25 civilians were wounded as Russian forces shelled Kramatorsk, a town that in April suffered a missile strike on a train station that killed dozens of evacuating civilians.

A school and a kindergarten were seriously damaged in the new attack, the town's mayor said. Reuters could not independently verify the casualties or damage.

More than five million Ukrainians have fled abroad since Russian President Vladimir Putin launched the invasion on Feb. 24. Millions more are displaced inside Ukraine.

Russia calls its actions in Ukraine a "special operation" to disarm Ukraine and protect it from fascists. Ukraine and the West say the fascist allegation is baseless and that the war is an unprovoked act of aggression.

As Western military aid for Ukraine pours into the country, the United States has also provided crucial intelligence that has helped Ukrainian forces kill Russian generals, the New York Times reported on Wednesday.

Washington has provided to Ukraine details on the location of Russia's mobile military headquarters, allowing Ukrainian forces to strike those targets, the newspaper said, citing senior U.S. officials.

The Pentagon and the White House did not immediately respond to Reuters' requests for comment on the report.

Ukrainian officials said they have killed about 12 Russian generals on the battlefield, according to the New York Times.

Ukraine's military said on Thursday its forces had repelled 11 Russian attacks, downed four Russian aircraft and destroyed over a dozen Russian military vehicles, including tanks.

Russian missile strikes in recent days have included railway stations in an attempt to interdict Western arms transfers.

OIL BAN?

The United States and its European allies have slapped sweeping sanctions on Moscow over the invasion and provided Ukraine with billions of dollars worth of aid, including arms.

A source said European Union envoys could reach a deal as early as Thursday on a plan to phase out imports of Russian crude oil within six months and refined products by the end of this year. It requires agreement by all 27 EU governments.

The plan also targets Russia's top bank, its broadcasters, and hundreds of individuals. It would follow U.S. and British oil bans and be a watershed for the EU, the world's largest trading bloc, which remains dependent on Russian energy and must find alternative supplies.

The Kremlin said Russia was weighing various responses to the EU plan, which it said would be costly for European citizens.