Ukrainian President Volodymyr Zelenskyy warned earlier this week that Russia was likely to intensify its "hostile activity", as Kyiv awaits a historic decision from the European Union on its membership application.
Nearly three months after Russia launched an invasion of his country, Zelenskyy said there had been "few such fateful decisions for Ukraine" as the one it expects from the EU this week, adding in his evening address that "only a positive decision is in the interests of the whole of Europe."
"Obviously, we expect Russia to intensify hostile activity this week ... We are preparing. We are ready," he continued.
Ukraine said it had also repulsed fresh attacks by Russian forces on the eastern front, rocked by weeks of fierce battles.
Earlier, Zelenskyy vowed his troops would not give up the south of the country, after he visited the frontline there.
NATO's chief Jens Stoltenberg had warned that the war could grind on "for years" and urged Western countries to be ready to offer long-term military, political and economic aid.
"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," Stoltenberg told German daily newspaper Bild.
Ukraine has repeatedly urged Western countries to step up their deliveries of arms since the February 24 invasion, despite warnings from nuclear-armed Russia that it could trigger wider conflict.
Zelensky spoke after making a rare trip outside Kyiv a day earlier to the hold-out Black Sea city of Mykolaiv, where he visited troops nearby and in the neighbouring Odessa region for the first time since the 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.
Mykolaiv is a key target for Russia as it lies on the way to the strategic port of Odessa.
The Ukraine war is fuelling not only a global food crisis but an energy crisis too.
Hit by punishing sanctions, Moscow has turned up the pressure on European economies by sharply reducing gas supplies, which has in turn sent energy prices soaring.
Germany announced emergency measures including increased use of coal to ensure it meets its energy needs after a drop in the supply of Russian gas.
Austria was also turning to coal, with its government announcing that it will reopen a mothballed coal power station to combat the shortages - though the process could take months.
Italian company Eni meanwhile joined a huge Qatari project to expand production from the world's biggest natural gas field, days after Russia slashed supplies to Italy.
The worst of the fighting continues to be in the eastern industrial Donbas region, with battles raging in villages outside the city of Severodonetsk, under unrelenting Russian fire for weeks.
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