LVIV, Ukraine (NewsNation) — President Joe Biden confirmed Russia deployed a hypersonic weapon in Ukraine, which experts say has never been used in combat.

The missile is capable of flying at five times the speed of sound, and could deliver a nuclear weapon.

Hypersonic weapons are “the only thing that they can get through (Ukranian defenses) with absolute certainty,” Biden said.

The shelling of major Ukrainian cities continued Monday. Ukraine officials in Mariupol rejected a Russian demand Monday to lay down arms and raise white flags in exchange for safe passage out of the besieged city.

“There can be no talk of any surrender, laying down of arms,” Ukrainian Deputy Prime Minister Irina Vereshchuk told the news outlet Ukrainian Pravda. “We have already informed the Russian side about this.”

Russian Col. Gen. Mikhail Mizintsev had offered two corridors, one heading east toward Russia and the other west to other parts of Ukraine. He did not say what Russia planned if the offer was rejected.

Mariupol has seen some of the worst horrors of the war in the four weeks since the start of the invasion.

Ukraine’s prosecutor general said Russians struck a chemical plant outside the eastern city of Sumy just after 3 a.m. Monday, causing a leak in a 50-ton tank of ammonia that took hours to contain. Overnight, Konashenkov said a cruise missile strike hit a military training center in the Rivne region of western Ukraine.

Russian military spokesman Igor Konashenkov claimed the leak was a “planned provocation” by Ukrainian forces to falsely accuse Russia of a chemical attack.

Vitaliy Koval, the head of the Rivne regional military administration, confirmed a twin Russian missile strike on a training center there early Monday but offered no details about injuries or deaths.

Ukraine’s nuclear regulatory agency said Monday that radiation monitors around the Chernobyl nuclear power plant, site of the world’s worst meltdown in 1986, have stopped working.

The agency said that, and a lack of firefighters to protect the area’s radiation-tainted forests as the weather warms, could mean a “significant deterioration” in the ability to control the spread of radiation in Ukraine and beyond. Management at the plant said Sunday that 50 staff members who had been working nonstop since the Russian takeover have been rotated out and replaced.

In the capital, Kyiv, Russian shelling devastated a shopping center near the city center, killing at least eight people and leaving a sea of rubble amid scarred high-rises. Ukrainian authorities also said Russia bombed a chemical plant in northeastern Ukraine and hit a military training base in the west with cruise missiles.

Ukrainian professor Martina Shuvalova, a Kyiv resident, told “NewsNation Prime” on Monday that the people of her city have gotten so used to the constant wailing of air raid sirens that they are no longer “willing to run to the bomb shelter” at every alert.

“We are not able to sleep in the night (for) almost a month,” she said. “People are having headaches; they’re exhausted.” As for the condition of the city, she said, “in pictures and in video, it’s really terrible. But in real life, it’s much, much worse.”

Multiple attempts to evacuate residents from Mariupol and other Ukrainian cities have failed or only partly succeeded, with bombardments continuing as civilians tried to flee. Mariupol officials said at least 2,300 people have died in the siege.

On Sunday, strikes hit an art school sheltering some 400 people. The strike on the art school was the second time in less than a week that officials reported an attack on a public building where Mariupol residents had taken shelter. On Wednesday, a bomb hit a theater where more than 1,000 people were believed to be sheltering. At least 130 people were reported rescued on Friday, but there has been no update since then.

City officials and aid groups say food, water and electricity have run low in Mariupol and fighting has kept out humanitarian convoys.

The fall of Mariupol would allow Russian forces in southern and eastern Ukraine to unite. But Western military analysts say that even if the city is taken, the troops battling a block at a time for control there may be too depleted to help secure Russian breakthroughs on other fronts.

Mariupol has become a focal point of Russia’s assault on Ukraine, but attacks were also reported to have intensified on the country’s second city Kharkiv on Monday.

U.S. Defense Secretary Lloyd Austin said Ukrainian resistance means Russian President Vladimir Putin’s “forces on the ground are essentially stalled.”

President Joe Biden discussed Russia’s “brutal tactics” in Ukraine with European leaders on Monday and Britain said they reaffirmed their commitment to support Ukraine militarily, diplomatically and economically.

But European Union foreign ministers disagreed on whether and how to include energy in sanctions, with Germany saying the bloc was too dependent on Russian oil to declare an embargo.

Biden is heading later in the week to Brussels and then Poland for in-person talks.

The Russian Foreign Ministry warned Monday that relations with the U.S. are “on the verge of a breach,” citing “unacceptable statements” by Biden about Putin being a war criminal.

The U.N. has confirmed 902 civilian deaths in the war but concedes the actual toll is likely much higher. It says nearly 3.4 million people have fled Ukraine. The Ukrainian prosecutor general’s office says at least 115 children have been killed and 148 injured.