BRUSSELS (AP) — Ukraine's armed forces have made significant early gains in their counter-offensive against Russian troops in southern and eastern Ukraine but fighting appears set to drag on for months, U.S. Secretary of State Antony Blinken and the head of NATO said Friday.

Blinken, who was at NATO headquarters to brief the 29 U.S. allies after a trip to Kyiv on Thursday, said the six-month war in Ukraine is entering a critical period. He urged the conflict-torn country’s Western backers to maintain their support through the winter.

“The initial signs are positive, and we see Ukraine making real, demonstrable progress in a deliberate way,” Blinken said, referring to the Ukrainian military's recent push into Russian-occupied areas in southern Ukraine and the eastern Donbas region.

“But this is likely to go on for some significant period of time,” he said. “There are a huge number of Russian forces that are in Ukraine, and unfortunately, tragically, horrifically, President (Vladimir) Putin has demonstrated that he will throw a lot of people into this at huge cost to Russia.”

NATO Secretary-General Jens Stoltenberg said the invasion launched by Putin in February is “entering a critical phase."

“Ukrainian forces have been able to stall Moscow’s offensive in Donbas, strike back behind Russian lines and retake territory,” he said.

But Stoltenberg warned that allied unity will be tested in coming months, “with pressure on energy supplies and the soaring cost of living caused by Russia’s war.” He renewed calls for allies to supply special uniforms, generators, tents and equipment to help Ukraine’s army weather the winter.

Blinken appeared moved by his visit to Ukraine as he railed against what he said were Russian war crimes and the price of “indiscriminate violence” inflicted on civilians.

“I saw the costs in my visit to a children’s hospital in Kyiv, where I met kids who will spend the rest of their lives without limbs, or with enduring brain injuries, or with other trauma that may be invisible to the eye, because of atrocities committed by Russian forces,” he said.

The one-day visit was Blinken’s second to Ukraine’s capital since the war began, and his fifth into Ukraine since becoming secretary of state. On his last trip, in April, he traveled on the same overnight train with Defense Secretary Lloyd Austin but did not have the opportunity to see much of the damage in and around the city caused by Russian shelling.

At the hospital, Blinken met with, among other children wounded in aerial and artillery attacks, a six-year old girl named Maryna who lost a leg after a rocket struck her house in the city of Kherson. He also toured the town of Irpin, much of it devastated by repeated Russian air strikes.

“You see just miles from downtown Kyiv these bombed-out buildings, civilian dwellings,” he said after his return. “The only thing you can say when you see it is, at best – at best, these were indiscriminate attacks on civilian buildings, and at worst, intentional, deliberate, designed to terrorize the population.”

“There has to be accountability for those who committed atrocities,” Blinken said.

At NATO on Friday, Blinken said Putin is using every weapon he has, including energy, to try to “break the will” of the allies, but that there is “a growing recognition around the world that while the costs of standing up to the Kremlin’s aggression are high, the costs of standing down would be even higher.”

___

Follow all AP stories on the war in Ukraine at https://apnews.com/hub/russia-ukraine.

Copyright 2022 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.