Zelenskiy Calls On Global Community To Condemn Russian 'Terrorist State' Following Discovery Of Mass Burial Site.

Ukrainian soldiers ride on a Russian armored personnel carrier in the liberated city of Izyum on September 16.

The NATO military alliance said it would support Ukraine in its fight against Russia “for as long as it takes” after Ukrainian President Volodymyr Zelenskiy stepped up calls for Western sanctions against Moscow following the discovery of a mass burial site in a city once occupied by Russian forces.

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NATO military committee Chairman Admiral Rob Bauer on September 17 said Western military aid was making a crucial difference as Ukraine conducts a powerful counteroffensive to retake occupied lands in the east and south of the country.

"The ammunition, equipment, and training that allies and other nations are delivering are all making a real difference on the battlefield," he said at a meeting in Tallinn.

"With its successes on the ground and online, Ukraine has fundamentally changed modern warfare," he added, citing both military and civilian actions.

Bauer said NATO would support Ukraine for "as long as it takes. Winter is coming but our support shall remain unwavering."

The reaffirmation of support came as Zelenskiy called on the global community to condemn the Russian "terrorist state” following the discovery of a mass burial site and evidence of torture in Izyum days after the city was retaken from Russia.
Speaking in his nightly video address on September 16, Zelenskiy said Russia should be punished with tougher sanctions.

"There is already clear evidence of torture, humiliating treatment of people. Moreover, there is evidence that Russian soldiers, whose positions were not far from this place, shot at the buried just for fun," he said.

Zelenskiy compared the discoveries made in Izyum this week with the Bucha massacre in the spring and reiterated his call for an international tribunal to be set up to hold Russia accountable for any crimes it committed in Ukraine.

The Ukrainian Defense Ministry has said that at least 440 bodies had been found at the site in Izyum.

The UN Human Rights Office said it planned to send investigators to Izyum.

White House National Security Council spokesman John Kirby described the reports as "repugnant" but said they were "in keeping with the kind of depravity and the brutality with which Russian forces have been prosecuting this war."

The Czech Republic, which currently holds the rotating EU Presidency, called for the creation of an international war crimes tribunal after the new mass burial sites were found.

"Russia left behind mass graves of hundreds of shot and tortured people in the Izyum area. In the 21st century, such attacks against the civilian population are unthinkable and abhorrent," Czech Foreign Minister Jan Lipavsky said on Twitter .

"We must not overlook it. We stand for the punishment of all war criminals," he added.

Moscow has not commented on the mass burial site in Izyum, which was a Russian frontline stronghold before Ukraine's counteroffensive forced its forces to flee.

Reacting to the reports, U.S. Army General Mark Milley, chairman of the Joint Chiefs of Staff, said war crimes in Ukraine cannot be hidden.

"In terms of the totality of the scale [of potential war crimes], I don't know. But I would tell you that the world will discover that. War crimes cannot be hidden, especially things like mass graves," Milley told reporters traveling with him after arriving in Estonia for a NATO gathering.

Milley lauded Ukraine's military for seizing the "strategic initiative" from Russia -- suggesting that Ukraine had momentum in the war.

Asked whether Ukraine would be able to retake all its territory, Milley said: "The offensives are in the early stages. We're only looking at probably about two weeks so far. And it remains to be seen how far the Ukrainians can press this fight. So I think we'll have to wait and see how the fighting develops."

Elsewhere, the UN atomic watchdog said the Russian-occupied Zaporizhzhya nuclear power plant has been reconnected to the Ukrainian national grid after one of its four power lines was repaired.

The plant had been completely shut down a week ago amid heavy fighting in the area, raising fears of a potential radiation disaster. Russia has taken control of the plant, but it is still operated by Ukrainian personnel.

Near the city of Zaporizhzhya, which is still under Ukrainian control, the Vatican reported that papal envoy Cardinal Konrad Krajewski came under light arms fire as he delivered humanitarian aid in the name of Pope Francis. No one was hurt and it was not clear where the shots came from.

The cardinal is scheduled to visit Kharkiv after previously traveling to Odesa.

WATCH: The speed and efficiency of Ukraine's counteroffensive in the northeastern region of Kharkiv came as a stunning surprise to the Russian military. Ukraine went to great lengths to keep its counteroffensive secret, including deliberately deceiving Russian forces about its military maneuvers. RFE/RL spoke to some of the soldiers involved, who described their tactics.

Meanwhile, Russia’s TASS news agency quoted local authorities in Russia's Belgorod region as saying Ukrainian shelling from across the border had killed one person in the area. The report could not be independently verified.

Ukrainian authorities say that Russian forces have used the border region to fire missiles into nearby Kharkiv, Ukraine’s second-largest city.

In a Twitter update on September 17, British military intelligence said Ukraine continued its offensive operations in the northeast of the country while Russian forces have established a defensive line between the Oskil River and the town of Svatove.

"Russia likely sees maintaining control of this zone as important because it is transited by one of the few main resupply routes Russia still controls from the Belgorod region of Russia," the Defense Ministry said on Twitter.

"Russia will likely attempt to conduct a stubborn defense of this area, but it is unclear whether Russia's frontline forces have sufficient reserves or adequate morale to withstand another concerted Ukrainian assault," it added.

With reporting by RFE/RL’s Ukrainian Service, Reuters, dpa, AP, and AFP