While Ukraine remains defiant, NATO Secretary-General Jens Stoltenberg urged Western countries must be ready to offer long-term military, political and economic support to Kyiv during a grinding war.
"We must be prepared for this to last for years," Stoltenberg told German daily newspaper Bild.
The NATO chief added "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 "Time is now the vital factor," he wrote in a Sunday Times article, calling for the West to ensure Ukraine has the "strategic endurance to survive and eventually prevail."
Ukraine has repeatedly urged Western countries to step up their deliveries of arms since the February 24 invasion, despite Russian warnings that it could trigger wider conflict.
Russia's defense ministry said Sunday it launched missile strikes during the past 24 hours, with one attack by Kalibr missiles on a top-level Ukrainian military meeting near the city of Dnipro killing "more than 50 generals and officers."
Moscow also claimed it hit a depot in Mykolaiv, destroying "ten 155 mm howitzers and around 20 armoued vehicles supplied by the West to the Kyiv regime over the last ten days", the Russian defense ministry said.
There was no independent verification of the claims.
Mykolaiv is a key target for Russia as it lies on the way to the strategic port of Odessa.
With Russia maintaining a blockade of Odessa that has trapped grain supplies and is threatening a global food crisis, 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.
On Saturday, Ukraine President Vlodomyr Zelenskyy visited Mykolaiv and troops nearby and in the neighboring 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."
