Sharjah24 - AFP: NATO's chief warned that the war in Ukraine could last "for years" as President Volodymyr Zelensky vowed Sunday his forces would not give up the south of the country to Russia after he visited the frontline there.

Ukraine said it had also repulsed fresh attacks by Russian forces on the eastern front, rocked by weeks of fierce battles as Moscow tries to seize the industrial Donbas region.

While Ukraine remained 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.

"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".

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.