NATO's chief warned that the war in Ukraine could last "for years" as President Volodymyr Zelensky vowed Sunday that his forces would not give up the south of the country to Russia after his first visit to the frontline there.
Ukraine said it had also repulsed fresh attacks by Russian forces on the eastern front, where there have been weeks of fierce battles as Moscow tries to seize the industrial Donbas region.
While Ukraine remained defiant, NATO Secretary-General Jens Stoltenberg warned Western countries must be ready to offer long-term support to Kyiv during a grinding war.
"We must be prepared for this to last for years," Stoltenberg told German daily newspaper Bild.
"We must not weaken in our support of Ukraine, even if the costs are high -- not only in terms of military support but also because of rising energy and food prices."
British Prime Minister Boris Johnson issued a similar warning, urging sustained support for Kyiv or risk "the greatest victory for aggression" since World War II.
"Time is now the vital factor," Johnson wrote in an article for the Sunday Times after making his second visit to Kyiv, calling for the West to ensure Ukraine has the "strategic endurance to survive and eventually prevail".
- 'Return everything' -
Russian forces have directed their firepower at the east and south of Ukraine in recent weeks since failing in their bid to take the capital Kyiv after the lightning February 24 invasion.
Zelensky made a rare trip outside Kyiv Saturday to the hold-out Black Sea city of Mykolaiv, and visited troops nearby and in the neighbouring Odessa region for the first time since the Russian invasion.
"We will not give away the south to anyone, we will return everything that's ours and the sea will be Ukrainian and safe," he said in a video posted on Telegram as he made his way back to Kyiv.
He said he talked with troops and police during his visit.
"Their mood is confident, and looking into their eyes it is obvious that they all do not doubt our victory," he said.
But Zelensky admitted that losses were "significant", adding: "Many houses were destroyed, civilian logistics were disrupted, there are many social issues."
Mykolaiv is a key target for Russia as it lies on the way to the strategic Black Sea port of Odessa.
Blockaded by Russia, Odessa residents have turned their attention to rallying the home front effort.
"Every day, including the weekend, I come to make camouflage netting for the army," said Natalia Pinchenkova, 49, behind a large Union flag, a show of thanks to Britain for its support for Ukraine since the conflict erupted.
Soldiers in Mykolaiv meanwhile were trying to keep their pre-war routines alive, with one saying he would not give up his vegan diet on the frontlines.
Oleksandr Zhuhan said he had received a package from a network of volunteers to keep up his plant-based diet.
"There was pate and vegan sausages, hummus, soya milk... and all this for free," the 37-year-old drama teacher said happily.
- 'Hero' -
Back in Kyiv, with shockwaves from the war continuing to reverberate around the world, thousands gathered to pay tribute to one young man -- Roman Ratushny, a leading figure in Ukraine's pro-European Maidan movement, who was killed fighting Russians in the country's east earlier this month aged just 24.
In front of the coffin draped in a yellow and blue Ukrainian flag at the foot of a monument that overlooks the sprawling Independence Square in the capital, people of all ages saluted his memory.
"I think it is important to be here because he is a hero of Ukraine and we must remember him," Dmytro Ostrovsky, a 17-year-old high school student, told AFP.
The loss put a human face on the shared grief of Ukrainians, as the bloodshed continues.
The worst of the fighting continues to be in the eastern industrial Donbas region, with battles raging in villages outside the city of Severodonetsk, which Russia has been trying to seize for weeks.
"There's an expression: prepare for the worst and the best will come by itself," the governor of the eastern Lugansk region, Sergiy Gaiday, told AFP in an interview from the Ukrainian-controlled city of Lysychansk across the river from Severodonetsk.
"Of course, we need to prepare," he said, wearing a flak jacket and carrying gun cartridges and a tourniquet.
Ukraine's armed forces said Sunday they had pushed back Russian attacks on villages near Severodonetsk.
"Our units repulsed the assault in the area of Toshkivka," the Ukrainian army said on Facebook. "The enemy has retreated and is regrouping."
It said Russian forces were "storming" towards the village of Orikhove, but that it had "successfully repulsed" an assault near the village.
In Lysychansk, the governor Gaiday said watching his home city, Severodonetsk, be shelled and people he knew dying was "painful".
"I'm a human being but I bury this deep inside me," he said, adding that his task is to "help people as much as possible".