TORETSK, Ukraine (AP) — Russia pounded eastern Ukraine on Tuesday as the U.S. defense secretary promised to "keep moving heaven and earth" to get Kyiv the weapons it needs to repel the new offensive even as Moscow warned such support risked widening the war.

Two months into the devastating conflict, Western arms have already helped Ukraine stall Russia's invasion — but its leaders have said they need more support fast.

U.S. Defense Secretary Lloyd Austin said that help was on the way, as he convened a meeting of officials from around 40 countries at the United States' Ramstein Air Base in Germany to pledge more weapons. Germany announced it cleared the way for delivery of Gepard anti-aircraft guns to Ukraine.

"This gathering reflects the galvanized world," Austin said in his opening remarks. He added that he wanted officials to leave the meeting "with a common and transparent understanding of Ukraine's near-term security requirements because we're going to keep moving heaven and earth so that we can meet them."

After fierce defense by Ukrainian forces thwarted Russia's attempt to take Ukraine's capital early in the war, Moscow now says its focus is the Donbas, the mostly Russian-speaking industrial region in eastern Ukraine. That move is already having a devastating effect on civilians trapped in the conflict.

In the small city of Toretsk, residents are struggling to survive, collecting rainwater for cleaning and washing up and fervently hoping for an end to the fighting.

"It's bad. Very bad. Hopeless," said Andriy Cheromushkin. "You feel so helpless that you don't know what you should do or shouldn't do. Because if you want to do something, you need some money; and there is no money now."

With the potentially pivotal battle for the Donbas underway, the U.S. and its NATO allies are scrambling to get artillery and other heavy weaponry to that area in time to make a difference.

German Defense Minister Christine Lambrecht said her government decided on Monday to clear the delivery of Gepard self-propelled armored anti-aircraft guns to Ukraine, though she didn't give details. German Chancellor Olaf Scholz has faced mounting pressure, including from within his governing coalition, to approve sending heavy weapons such as tanks and other armored vehicles to Ukraine.

Austin also noted Tuesday that more than 30 allies and partners have joined the U.S. in sending security assistance to Ukraine and more than $5 billion worth of equipment committed.

The meeting in Germany comes after Russian Foreign Minister Sergey Lavrov, speaking on Russian television, warned weapons supplied by Western countries "will be a legitimate target," and accused NATO of "pouring oil on the fire" with its support for Ukraine, according to a transcript on the Russian Foreign Ministry's website.

Lavrov also warned against provoking World War III and said the threat of a nuclear conflict "should not be underestimated."

Russian President Vladimir Putin has cited NATO's expansion and the risk that Kyiv could join the alliance as reasons for his invasion.

U.K. Armed Forces Minister James Heappey rejected Lavrov's accusations of NATO aggression as "utter nonsense."

He said "the reason there is a war in Ukraine right now is because Russia rolled over the borders of a sovereign country and started to invade their territory."

Heappey also said Russia was making "unsound" military decisions and giving away tactical advantages because of Putin's desire to secure some kind of victory by May 9, when Russia marks its victory in World War II.

Amid the talk of arms shipments, diplomatic efforts to seek an end to the fighting also continued. United Nations Secretary-General António Guterres met Lavrov on Tuesday and called again for a cease-fire. The U.N. chief is scheduled to meet Putin later.

Elsewhere, International Atomic Energy Agency Director General Rafael Mariano Grossi visited the Chernobyl nuclear plant to deliver equipment, conduct radiological assessments and restore safeguards monitoring systems after tanks and troops churned up highly contaminated soil there in the early hours of Russia's invasion in February. His visit comes on the anniversary of the disaster at the plant in 1986, the world's worst nuclear accident.

In its latest assessment of the fighting, the British Defense Ministry reported Russian advances and heavy fighting in the Donbas region, with one town, Kreminna, reportedly falling after days of street-to-street fighting.

Ukraine's General Staff said Russian forces shelled Kharkiv, the country's second-largest city that lies outside the Donbas but has seen significant attacks as Moscow seeks full control of the region. Ukrainian forces struck back in the Kherson region in the south.

A senior Russian military official has said that Russia's goal is full control of Ukraine's east and south, which would give it a swath of land that lies between Russia and Crimea, which Moscow seized in 2014.

Four people died and nine more were wounded on Monday in the Russian shelling of the Donetsk region of the Donbas, its governor Pavlo Kyrylenko said on Telegram. He said a 9-year-old girl and a 14-year-old boy were among those killed.

The city council and mayor of Mariupol said a new mass grave was identified about 10 kilometers (6 miles) north of the port city, which is key to the battle of the Donbas. Mayor Vadym Boychenko said authorities were trying to estimate the number of victims. It was at least the third new mass grave discovered in Russian-controlled areas near Mariupol in the last week.

Mariupol has been gutted by bombardment and fierce street fighting over the past two months. Russia's capture of the city, where an estimated 2,000 Ukrainian troops and some 1,000 civilians are reportedly sheltering in a sprawling steel works, would deprive Ukraine of a vital port, help complete the land corridor to Crimea and free up troops to redeploy elsewhere in the Donbas.

Britain said it believes 15,000 Russian troops have been killed in Ukraine since Russia's invasion began — far above the 1,351 deaths acknowledged by Moscow. Defense Secretary Ben Wallace said 25% of the Russian combat units sent to Ukraine "have been rendered not combat effective."

Ukrainian officials have said about 2,500 to 3,000 Ukrainian troops had been killed as of mid-April.

The West hopes that boosting arms supplies will help remaining fighters repel Russia's invasion.

As he opened the meeting in Germany, Austin sought to reassure Kyiv: "We know, and you should know, that all of us have your back and that's why we're here today — to strengthen the arsenal of Ukrainian democracy."

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Gambrell reported from Lviv, Ukraine. Associated Press journalist Yuras Karmanau in Lviv, Ukraine, and David Keyton in Kyiv, Ukraine, and AP staff around the world contributed to this report.

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Follow the AP's coverage of the war at https://apnews.com/hub/russia-ukraine