(NewsNation) — Russia continues to shell Ukrainian cities as it pours more troops into the war, seeking to slice the country in two as the battle for control of the eastern industrial heartland continues. This comes as the U.N. announced more than five million residents have fled the country.

The fighting unfolded throughout the country’s eastern Donbas region. If successful, it would give President Vladimir Putin a victory following the failed attempt by Moscow’s forces to storm the capital, Kyiv.

The Ukrainian General Staff said Wednesday that Russia was continuing to mount offensives at various locations in the east as its forces probe for weak points in the Ukrainian lines.

In Mariupol, the devastated port city near the Donbas, Ukrainian troops said the Russian military dropped heavy bombs to flatten what was left of a sprawling steel plant, believed to be the defenders’ last holdout, and hit a hospital where hundreds were staying.

Ukrainian soldiers in the steel plant pleaded for help in a video Wednesday, saying, “We may have only a few days or hours left.”

The battle to control the mostly Russian-speaking Donbas region has turned in Russia’s favor.

Russia now controls 80% of the region, Luhansk governor Serheii Haidai said. Kyiv controlled 60% of the region when Russia invaded Feb. 24.

Also Wednesday, Ukraine is expected to receive much-needed weaponry and warplanes to support resistance efforts. As part of President Joe Biden’s $800 million aid package authorized last week, the country will receive 155-mm howitzers, 40,000 artillery rounds and 11 Soviet-designed Mi-17 helicopters.

Deputy Prime Minister Iryna Vereshchuk said that there was a “preliminary” agreement to open a humanitarian corridor for women, children and the elderly to leave Mariupol for the Ukraine-controlled city of Zaporizhzhia. She said on the the messaging app Telegram that civilians in Mariupol were facing a “catastrophic humanitarian situation.”

Vereshchuk previously said no agreement had been reached with Russia on an evacuation route on each of the past three days. There was no immediate confirmation from the Russian side, which issued a new ultimatum to the Ukrainian defenders to surrender Wednesday after a previous ultimatum was ignored.

The Russian Defense Ministry said those who surrender will be allowed to live and given medical treatment. The Ukrainian troops have repeatedly vowed not to give up.

The UN says that of the refugees who’ve fled Ukraine, more than half have moved to Poland. It estimates more than seven million Ukrainians have been displaced.

Key to the Russian campaign is the capture of Mariupol, which would deprive Ukraine of a vital port and complete a land bridge between Russia and the Crimean Peninsula, seized from Ukraine in 2014. It would also free up Russian troops to attack other targets in the region, including mines, metals plants and heavy-equipment factories.

A few thousand Ukrainian troops, by the Russians’ estimate, remained holed up in the sprawling steel plant. The deputy commander of the Azov regiment, who was among the troops remaining in Mariupol, said the Russian military dropped heavy bombs on the steel plant and hit an “improvised” hospital.

Serhiy Taruta, the former governor of the Donetsk region and a Mariupol native, also reported the bombing of the hospital, where he said 300 people, including wounded troops and civilians with children, were sheltered.

The eastern cities of Kharkiv and Kramatorsk also came under attack Wednesday. Russia said it struck areas around Zaporizhzhia and Dnipro west of the Donbas with missiles. Those claims could not be independently verified.

Both sides have described the assault that began Monday as a new phase of the war.

“They have driven almost everyone and everything that is capable of fighting us against Ukraine,” Ukrainian President Volodymyr Zelenskyy said in an overnight address.

Despite claims that they are hitting only military sites, Russians continue to target residential areas and kill civilians, he said. Zelenskyy also said the Kremlin has not responded to a proposal to exchange Viktor Medvedchuk, the jailed leader of a pro-Russia party, for the Mariupol defenders.

A senior U.S. defense official, speaking on condition of anonymity to discuss the Pentagon’s assessments of the war, said the Russians had added two more combat units, known as battalion tactical groups, in Ukraine over the last 24 hours. That brought the total units in the country to 78, all of them in the south and the east, up from 65 last week, the official said.

That would translate to 55,000 to 62,000 troops, based on what the Pentagon said at the start of the war was the typical unit strength of 700 to 800 soldiers. But accurately determining Russia’s fighting capacity at this stage is difficult.

Eyewitness accounts and reports from officials have given a broad picture of the extent of the Russian advance. But independent reporting in the parts of the Donbas held by Russian forces and separatists is severely limited, making it difficult to know what is happening in many places on the ground.

A European official, likewise speaking on condition of anonymity to discuss military assessments, said Russia also has 10,000 to 20,000 foreign fighters in the Donbas. They are a mix of mercenaries from Russia’s private Wagner Group and Russian proxy fighters from Syria and Libya, according to the official.

Analysts say the offensive in the east could devolve into a war of attrition as Russia runs up against Ukraine’s most experienced, battle-hardened troops, who have fought pro-Moscow separatists in the Donbas for eight years.

Biden is expected to announce a new weapons package in the coming days that will include additional artillery and ammunition, according to a U.S. official, who was not authorized to comment publicly and spoke on the condition of anonymity. Canada and the Netherlands also planned to send more heavy weapons, their prime ministers said.

Military experts said the Russians’ goal is to encircle Ukrainian troops from the north, south and east.

Russia said Wednesday that it has presented Ukraine with a draft document outlining its demands as part of talks aimed at ending the conflict days after Putin said the negotiations were at a “dead end.”

Kremlin spokesman Dmitry Peskov Peskov said during a conference call with reporters that “the ball is in [the Ukrainians’] court, we’re waiting for a response.” It was not clear when the Russian document was sent or if it offered anything new to the Ukrainians, who presented their own demands last month.