Ukrainian President Volodymyr Zelenskiy said Russian forces were trying to advance in the northeast and east and "planning something" in the south, while NATO sought on Wednesday to reassure other countries that fear destabilisation from Moscow.
Ukraine's General Staff said its forces had repelled six Russian attacks in the past 24 hours in the eastern Donbas region, while Russian artillery had relentlessly shelled the right bank of the Dnipro River and Kherson city further south.
Winter weather has hampered fighting on the ground, and Zelenskiy has told Ukrainians to expect a major Russian barrage this week on Ukraine's stricken electricity infrastructure, which Moscow has pounded roughly weekly since early October.
He said the Russian military was attacking the Donbas regions of Donetsk and Luhansk in the east as well as Kharkiv in the northeast, where Ukraine pushed back Russian forces in September.
"The situation at the front is difficult," he said in his nightly video address. "Despite extremely large losses, the occupiers are still trying to advance" in Donetsk, Luhansk and Kharkiv. And "they are planning something in the south," he said, without elaborating.
Reuters could not independently verify the latest battlefield reports.
Foreign ministers from the NATO alliance, including US Secretary of State Antony Blinken, were set to focus on helping fragile countries concerned about their own stability amid an energy crisis prompted by the Ukraine war.
Moldova, Georgia and Bosnia are all "facing pressure from Russia" NATO Secretary General Jens Stoltenberg said on Tuesday.
The ministers began their two-day meeting in Bucharest on Tuesday with pledges both to help Ukrainians cope with what the defence alliance's chief said was Moscow using winter weather as "a weapon of war" and to help sustain Kyiv's military campaign.
"In a nutshell: Patriots (missile defence systems) and transformers (for our energy needs) are what Ukraine needs the most," Ukrainian Foreign Minister Dmytro Kuleba told reporters on the sidelines of the NATO meeting.
Former Russian president Dmitry Medvedev, now deputy head of Moscow's security council and a prominent hawk, warned NATO against providing Ukraine with Patriot systems and denounced the Atlantic alliance as a "criminal entity" for delivering arms to what he called "Ukrainian fanatics".
Stoltenberg said allies were discussing providing Patriot units but that they would need to be maintained and provided with ammunition, which was a "huge challenge" in itself.
Washington pledged $53 million to buy power grid equipment and U.S. President Joe Biden said providing more military assistance was a priority. Republicans, who take control of Congress' House of Representatives in January, have talked about pausing the funding, which has exceeded $18 billion.