ODESSA, Ukraine — Ukrainian forces conducted counteroffensives against Russian positions on Wednesday, seeking to inflict what one official called “maximum casualties,” even as the Russian military invasion intensified its deadly attacks on cities. .

In Mariupol, an airstrike destroyed a theater where around 1,000 people had taken refuge, according to city and regional administrators, and photos and videos posted online showed the burning wreckage of the building. Officials in Mariupol, the beleaguered southern city that suffered the most intense shelling, said they could not yet estimate the number of civilian casualties, who may have been in a bomb shelter under the theater .

After coming under relentless hammering in the first weeks of the war, Ukrainian troops attempted to regain some momentum with counterattacks against Russian positions outside kyiv and in the Russian-occupied city of Kherson in southern Ukraine, a senior Ukrainian military official said.

Credit…Donetsk Regional Administration, via Reuters

Rather than seek to regain lost territory, Ukrainian forces tried to cause as much destruction and death as possible, attacking Russian troops and equipment with tanks, warplanes and artillery, said the official, speaking on condition of anonymity to discuss sensitive military information.

“In the task of inflicting maximum casualties, we have done an excellent job,” the official said.

While Ukrainian President Volodymyr Zelensky pleaded with Congress for more aid and President Biden promised more weapons, Russian President Vladimir V. Putin falsely accused Ukraine of seeking weapons of mass destruction and claimed that what he called an “economic blitzkrieg” by the West, aimed at destroying Russia, had failed.

Mr Putin also mocked Russians who oppose the war, saying the Russian people could tell ‘true patriots from scum and traitors, and just spit them out like a gnat that accidentally flew into their mouths’ .

Ukrainian and Russian negotiators held a third consecutive day of talks on a possible settlement of the conflict, and typically the Kremlin left a muddy picture of its intentions. Mr Putin’s bellicose, often false statements, peppered with World War II references, clashed with more conciliatory comments from his underlings.

But little seemed to have changed on the battlefield. The war in Ukraine, about to enter its fourth week, has become a crushing daily grind with little evidence of significant gains for either side.

Details of the Ukrainian offensive could not be fully independently established, although several senior Ukrainian officials, including key aides to Mr. Zelensky, confirmed that the counterattacks were underway.

In Kyiv, missile and heavy artillery strikes sounded overnight and early Wednesday morning in exchanges in outlying suburbs that were noticeably heavier and noisier than on previous days. Two people were injured and a residential building was damaged in a strike that landed near the city zoo, the second time in two days that shells have landed near the city center.

Credit…Lynsey Addario for The New York Times

Satellite images on Tuesday showed thick black smoke over Kherson airport, where the senior military official said Ukrainian forces had targeted parked Russian military planes.

Kherson was the first (and so far only) major city to be fully captured by Russian forces, who turned it into a forward military base from which they launched attacks on towns and villages surrounding areas, according to Ukrainian officials. On Tuesday, the Russian Defense Ministry announced that it had taken control of the entire Kherson region, giving Russian forces an important foothold in southern Ukraine that the Ukrainian army will find difficult to dislodge.

Even so, neither side can be said to have made much progress militarily. The Institute for the Study of War, which closely follows developments, noted in an assessment Tuesday evening that for almost two weeks Russian forces have not carried out simultaneous attacks of large scale that would allow them to take control of several areas at once in Ukraine. And they are unlikely to do so next week, he added.

In the absence of significant military gains, Russian forces continued a campaign of terror against Ukrainian civilians on Wednesday.

At least 10 people were killed when a Russian strike hit a bread production line in Chernihiv, a town north of kyiv that has come under heavy shelling by Russian troops seeking to move to the capital . Ukraine’s attorney general’s office said in a statement that the attack happened around 10 a.m. as people lined up outside a grocery store. Photos released by the prosecutor’s office showed several bodies strewn across a dirt yard.

Using heavy artillery, cruise missiles and warplanes, Russian forces systematically targeted civilian areas with no military presence, striking apartment buildings, schools and hospitals in towns and villages on a broad front in northern, eastern and southern Ukraine. The attacks may have killed thousands of civilians, although an accurate death toll could not be established.

Saying it is “deeply concerned” about Russia’s use of force, the International Court of Justice on Wednesday ordered Russia to immediately suspend its military operations, pending its full review of a case submitted by Ukraine on last month. However, the order was not expected to lead to an immediate cessation of the assault.

According to the United Nations, at least 726 civilians have been killed, including 64 children, since the invasion began on February 24, although its figures do not include the areas where the fighting has been heaviest, such as Kharkiv and Mariupol. In Mariupol alone, which has been transformed into a hellish landscape of burnt and decimated buildings, local authorities say at least 2,400 people have been killed, and likely many more.

In Kharkiv, Ukraine’s second-largest city, the municipal emergency services agency first reported on Wednesday that 500 civilians had been killed since the start of the war, but later revised that number to 100 during the day. In any case, the agency said in a statement on Facebook, the true death toll could be much higher, noting that rescuers continued to search the rubble of residential neighborhoods for more bodies, often under the roof. fire.

Western defense and intelligence agencies estimate that each side suffered the deaths of thousands of fighters.

Mr. Zelensky’s appeal to Congress on Wednesday was in part a desperate effort to secure the weapons and defenses capable of repelling such attacks. At the heart of this appeal was a call for the imposition of a no-fly zone over Ukraine, aimed at preventing Russian fighter jets, which cause the most serious death and destruction, from to operate over Ukrainian territory. “Close the skies” has become a rallying cry for Ukrainian officials and ordinary citizens.

“Russia has turned the Ukrainian skies into a source of death for thousands of people,” Zelensky said.

Credit…Sarahbeth Maney/The New York Times

Knowing that the request was unlikely to be approved, given that it would plunge the American pilots into a direct confrontation with the Russians, Mr. Zelensky quickly pivoted to something that Republicans and Democrats were much more concerned about. receptive: asking for more weapons to allow its people to continue fighting on their own.

Mr Biden announced $800 million in new military aid to Ukraine, including anti-aircraft and anti-tank missiles, body armor, vehicles, drones and small arms, bringing the amount to $2 billion delivered or promised since the beginning of last year. But as expected, he did not offer to deliver fighter jets or impose a no-fly zone.

The United States and its allies have relied primarily on financial sanctions that are already devastating the Russian economy.

Mr Putin, in a televised videoconference with senior officials, once again incorrectly described the government in kyiv, led by a Jewish president and prime minister, as ‘pro-Nazi’ and on the way to acquire nuclear weapons. “Their target, of course, would have been Russia,” he said.

And then he went further into unreality, accusing the kyiv government of ignoring the suffering of the Ukrainian people whom their own forces were bombarding every day.

“The fact that people are dying, that hundreds of thousands, millions have become refugees, that there is a real humanitarian catastrophe in the cities held by neo-Nazis and armed criminals,” he said. declared. “They are indifferent.”

Russian officials closer to the talks said on Wednesday there had been signs of progress, although again the situation was unclear. They said the idea of ​​a neutral Ukraine, with status like that of Sweden or Austria, was on the table, which their Ukrainian counterparts disputed.

Sergey V. Lavrov, Russian Foreign Minister, told a Russian television channel that the status of the Russian language and Russian news outlets in Ukraine was under discussion and that “there are concrete formulas on about to be agreed”.

Mr. Zelensky has indicated that he is prepared to compromise on one of Russia’s central demands. In his daily video message, he said Ukraine “must recognize” that it will not join NATO. He added that the negotiations had become more “realistic”. But one of its negotiators, Mykhailo Podolyak, said Ukraine needed “absolute security guarantees”, including military support from its allies.

Michael Schwirtz reported from Odessa, Ukraine; Valerie Hopkins from Lviv, Ukraine; and Carlotta Gall from Kyiv. The report was provided by Anton Troyanovsky and Ivan Nechepurenko from Istanbul, and Richard Perez-Pena from New York.