KYIV, Ukraine • Russian forces tightened the noose around the defenders holed up Wednesday in a mammoth steel plant that represented the last known Ukrainian stronghold in Mariupol, as a fighter apparently on the inside warned in a video plea for help: “We may have only a few days or hours left.”

With the holdouts coming under punishing new bombing attacks, another attempt to evacuate civilians trapped in the pulverized port city failed because of continued fighting.

Meanwhile, the number of people fleeing the country topped 5 million, the Kremlin said it submitted a draft of its demands for ending the war, and the West raced to supply Ukraine with heavier weapons to counter the Russians’ new drive to seize the industrial east.

With global tensions running high, Russia reported the first successful test launch of a new type of intercontinental ballistic missile, the Sarmat. President Vladimir Putin boasted it can overcome any missile defense system and make those who threaten Russia “think twice,” and the head of the Russian state aerospace agency called the launch out of northern Russia “a present to NATO.”

The Pentagon described the test as “routine” and said it wasn’t considered a threat.

On the battlefield, Ukraine said Moscow continued to mount assaults across the east, probing for weak points in Ukrainian defensive lines. Russia said it launched hundreds of missile and air attacks on targets that included concentrations of troops and vehicles.

The Kremlin’s stated goal is the capture of the Donbas, the mostly Russian-speaking eastern region that is home to coal mines, metal plants and heavy-equipment factories. Detaching it would give Putin a badly needed victory two months into the war, after the botched attempt to storm the capital, Kyiv.

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 been fighting pro-Moscow separatists in the Donbas for the past eight years.

Russia said it presented Ukraine with a draft document outlining its demands for ending the conflict — days after Putin said the talks were at a “dead end.”

Kremlin spokesman Dmitry Peskov said that “the ball is in their court, we’re waiting for a response.” He gave no details on the draft, and it was not clear when it was sent or if it offered anything new to the Ukrainians, who presented their own demands last month.

Ukrainian President Volodmyr Zelensky said he had not seen or heard of the proposal, though one of his top advisers said the Ukrainian side was reviewing it.

Moscow has long demanded Ukraine drop any bid to join NATO.

Ukraine has said it would agree to that in return for security guarantees from a number of other countries. Other sources of tension include the status of the Crimean Peninsula, seized by Moscow in 2014, and eastern Ukraine, where the separatists have declared independent republics recognized by Russia.

In devastated Mariupol, Ukraine said the Russians dropped heavy bombs to flatten what was left of the sprawling Azvostal steel plant, believed to be the last pocket of resistance in the city.

A few thousand Ukrainian troops, by the Russians’ estimate, remained in the plant and its labyrinth of tunnels and bunkers spread out across about 4 square miles. Zelensky said about 1,000 civilians were also trapped there.

A Ukrainian posted a video plea on Facebook urging world leaders to help evacuate people from the plant, saying, “We have more than 500 wounded soldiers and hundreds of civilians with us, including women and children.”

The bodies of four people who died during the Russian occupation await burial Wednesday during funerals in Bucha on the outskirts of Kyiv.

the associated Press