Ukraine faces difficult months ahead and Russia's military capability should not be underestimated, NATO secretary general Jens Stoltenberg said on Monday.
Stoltenberg praised the "incredible courage" of Ukrainian forces following Russia's withdrawal from the strategic southern city of Kherson, and urged continued international support for Kyiv.
"The coming months will be difficult. Putin's aim is to leave Ukraine cold and dark this winter," he told a press conference in The Hague after meeting the Dutch foreign and defence ministers.
We should not make the mistake of underestimating Russia," Stoltenberg said, stressing that Moscow's forces "retain significant capabilities, as well as a large number of troops"."Russia has demonstrated the willingness to bear significant losses," Stoltenberg added.
Moscow's withdrawal from Kherson "demonstrates the incredible courage of the Ukraine armed forces but it also showed our continued support for Ukraine", Stoltenberg said.
The recapture of the city by Ukrainian troops is the latest in a string of setbacks for the Kremlin, which invaded Ukraine on February 24 hoping to achieve a lightning takeover and topple the government in days.
But Russian forces failed to capture the capital, Kyiv, and have since been pushed back from large portions of territory in the south and east.
Ukrainian President Volodymyr Zelensky on Monday visited the newly liberated city. On Sunday he said evidence had been uncovered of hundreds of new "war crimes" carried out by the Russian occupiers.
Stoltenberg said Russian forces had "shown extreme brutality".
"You have all seen the horrific scenes from the liberated territories and the indiscriminate attacks on civilians and critical infrastructure," Stoltenberg told reporters. It was not clear whether he referred to Kherson specifically.
The city of Kherson was the first major urban hub to fall to Russian forces and the only regional capital Moscow's troops gained control over.
Kremlin spokesman Dmitry Peskov on Monday declined to comment on Zelensky's visit to Kherson but insisted, "This territory is part of the Russian Federation."
Stoltenberg met Dutch Foreign Minister Wopke Hoekstra and Defence Minister Kajsa Ollongren to discuss the Netherlands's contribution to NATO and the war in Ukraine.
"We all now see, with the liberation of Kherson, that the Ukrainian strategy is working," Ollongren said.
"But winter is coming... and we must stay the course.
"If Russia stops fighting tomorrow, there is no more war anymore.
"If Ukraine stops fighting, there will be no more Ukraine," she said.
