Ukraine has made progress in retaking areas formerly held by Russian forces, but the length of the Russia’s war will depend on the assistance offered by Ukrainian allies, President Volodymyr Zelenskyy said.

Although Ukrainians are doing everything they can to resist and drive out Russia, “no one today can predict how long this war will last,” Zelenskyy said in his nightly address Friday.

“This will depend, unfortunately, not only on our people, who are already giving their maximum,” he said. “This will depend on our partners, on European countries, on the entire free world.”

He said Ukrainian troops have retaken over 1,000 “settlements” from Russian control, including six on Friday. They are attempting to restore electricity, running water, telephone communications and social services to those towns and villages, Zelenskyy said. He also said Ukraine on Friday shot down the 200th Russian aircraft since the invasion began.

MAP: Tracking Russia’s invasion of Ukraine

Russian shelling in the eastern Donetsk region, part of the Donbas region that Russia has been focused on, was responsible for a civilian death and 12 injuries on Friday, Pavlo Kyrylenko, a regional governor, said.

Russian forces also continued their attack on the east Friday, attacking new cities and towns, but failed to take the towns of Zolote and Kamyshevakha, the Ukrainian army said.

USA TODAY ON TELEGRAM: Join our Russia-Ukraine war channel to receive the latest updates straight to your inbox

Latest developments:

►U.S. Defense Secretary Lloyd Austin spoke with Russian Minister of Defense Sergey Shoygu on Friday, marking the first contact between the counterparts since the war began in late February.

►The U.S. is again accusing Russia of using the U.N. Security Council to spout disinformation and conspiracy theories about biological weapons in Ukraine to distract from its war in Ukraine. U.S. deputy ambassador Richard Mills called the Russian claims “categorically false and ludicrous.”

►A Swedish report released Friday laid out the pros and cons of obtaining NATO membership as the nation weighs the decision. The report listed Russian cyberattacks as one of the main risks of joining.

More than 600 children killed or injured since start of Russian invasion

Some 600 children have been killed or injured in Ukraine as a result of Russian aggression since mid-January, according to Ukraine’s prosecutor general’s office.

Since Jan. 14, 227 children have been killed and more than 420 injured in relation to the attacks on Ukraine, the office said in a Telegram post Saturday. Most of the children were killed or injured in the Donetsk region (139), followed by the Kyiv region (116) and the Kharkiv region (99).

The office cautioned that the numbers aren’t final, as death counts in areas of active combat or occupied territories cannot yet be made.

In addition, more than 1,700 educational institutions have been damaged in shellings by Russian forces. Some 144 of those were completely destroyed.

Russian troops withdrawing from battered Kharkiv

Russian troops are withdrawing from Ukraine’s second-largest city after weeks of heavy bombardment, the Ukrainian military said Saturday as Kyiv and Moscow’s forces engaged in a grinding battle for the country’s east.

Ukraine’s general staff said the Russians were pulling back from the northeastern city of Kharkiv and focusing on guarding supply routes, while launching mortar, artillery and airstrikes in the eastern Donetsk region in order to “deplete Ukrainian forces and destroy fortifications.”

Defense Minister Oleksii Reznikov said Ukraine was “entering a new – long-term – phase of the war.”

Russia’s offensive in the Donbas, Ukraine’s eastern industrial heartland, appeared to be turning into a village-by-village, back-and-forth slog with no major breakthroughs on either side. After failing to capture Kyiv, Ukraine’s capital, the Russian military decided to concentrate on the Donbas, but its troops have struggled to gain ground.

President Volodymyr Zelenskyy said Ukraine’s forces made progress, retaking six Ukrainian towns or villages in the past day. Western officials said Ukraine had driven Russian forces back around Kharkiv, which was a key target for Moscow’s troops.

CONGRESSIONAL AID:Sen. Rand Paul stalls $40 billion in aid for Ukraine, breaking with Mitch McConnell

‘Very difficult negotiations’ ongoing to get soldiers out of steel mill

Ukrainian leaders said the government is doing everything possible to negotiate for the evacuation of the wounded soldiers and remaining troops in the Azovstal steel mill in Mariupol.

“We’re talking about a large number of people. Of course, we are doing everything to evacuate all of the rest, each of our defenders. We have already brought in everyone in the world who can be the most influential mediators,” President Volodymyr Zelenskyy said in his nightly address Friday.

Deputy Prime Minister Iryna Vereshchuk said misinformation about the negotiations was making the process more difficult, and said officials are currently working on negotiations to rescue 38 “heavily wounded” soldiers. There is an estimated 600 military and wounded still holed up in the bunkers under the steel mill.

“The heart of the country now is Azovstal,” Vereschuk said in a social media post Friday. “Negotiating with the enemy is very difficult. The result may not please everyone. But our job is to get our boys out. All of you. Alive. God willing, everyone will be saved.”

US needs to approve Ukraine funding by May 19 to avoid disruptions

U.S. lawmakers will need to approve the next round of military aid money for Ukraine before May 19 to avoid disruptions in assistance being sent to Ukraine, Pentagon spokesperson John Kirby said.

President Joe Biden said in announcing the latest round of funding that the U.S. had “nearly exhausted” approved funds. Kirby said Friday there was about $100 million “that has not been allocated or announced.”

“We continue to urge the Senate to act as quickly as possible so that we don’t get to the end of May and not have any additional authorities to draw upon,” Kirby said.

This week Sen. Rand Paul blocked the passage of a $40 billion spending package for Ukraine, delaying until next week the attempt at fast-tracking an aid package that had bipartisan support. Paul wanted a provision added that would assign an inspector general to oversee how the billions are spent. Read more.

“By the 19th of May, it will start impacting our ability to provide aid uninterrupted,” Kirby said.”

Ukraine begins prosecuting alleged Russian war criminals

Ukraine’s prosecutor general said Friday that her office was readying 41 war crimes cases against Russian soldiers.

“We have 41 suspects in cases with which we will be ready to go to court. All of them concern Article 438 of the (Ukrainian) criminal code on war crimes, but different types of war crimes. There is the bombing of civilian infrastructure, the killing of civilians, rape and looting,” Iryna Venediktova said in a live briefing on Ukrainian TV on Friday evening.

It was not immediately clear how many of the suspects would be tried in absentia.

Friday marked the first war crime prosecution of a member of the Russian military in Kyiv, as a 21-year-old Russian soldier went on trial for the killing of an unarmed Ukrainian civilian in the early days of the war.

Venediktova said that two more of the suspects, who are physically in Ukraine, are likely to face preliminary hearings next week.

Contributing: The Associated Press