• Overnight Ukraine's air force said it had shot down 18 out of 25 Russian drones and one of two cruise missiles.
• With temperatures falling below freezing and Ukraine cloaked with snow, President Zelensky has said "winter as a whole is a new phase of war".
Ukrainian President Volodymyr Zelensky has said defences must be quickly beefed up across the front line, after meeting commanders in some of the main pressure points in the south and east.
"In all major sectors where reinforcement is needed, [we must] speed up building of structures," he said in his nightly address.
Russian forces are trying to encircle the eastern town of Avdiivka.
And they are targeting the southern regions of Kherson and Zaporizhzhia.
Overnight Ukraine's air force said it had shot down 18 out of 25 Russian drones and one of two cruise missiles.
With temperatures falling below freezing and Ukraine cloaked with snow, President Zelensky has said "winter as a whole is a new phase of war".
The Ukrainian leader said "maximum attention" would be paid to eastern towns coming under fire in the Donetsk region as well as a key defensive line in the north-east between Kupyansk and Lyman.
He also included the region around the capital Kyiv where fortifications would be bolstered.
President Zelensky's emphasis on strengthening defensive lines may lend weight to fears of an increasingly "frozen" conflict, despite some continued fierce fighting.
Ukraine counter-offensive since the summer is widely viewed as having failed to quickly deliver hoped-for gains.
Frontline morale on both sides will hinge to some extent on how well soldiers are equipped to cope with these colder months.
The military said 20 attacks had been repelled near Avdiivka alone and villages had come under attack around Bakhmut.
The industrial hub of Avdiivka has been almost encircled in recent weeks by Russian forces, who now control areas to the north and south, as well as the east of the town.
Dmytro Lazutkin, the spokesman for Ukraine's 47th Mechanised Brigade said the situation had become constantly difficult.
One community to the north-west of Avdiivka, Stepove, was coming under repeated attack, and Russia was sending significant forces in a bid to seize a nearby coke plant just outside Avdiivka.
"Without taking the coke plant, they can only dream about [capturing] Avdiivka... I'm not convinced they have such power to do that, although very many of them are concentrated there," he told Ukraine's public broadcaster.
In the south-east as well, Russian forces have sought to regain areas lost during Ukraine's counter-offensive around Robotyne, according to Ukrainian officials, who say they are managing to maintain positions they recaptured recently on the east bank of the River Dnipro.
Mr Zelensky said Ukraine was not backing down after its summer operations, although he was unhappy with the extent of casualties.
"We are losing people, I'm not satisfied. We didn't get all the weapons we wanted, I can't be satisfied," he told the Associated Press.
Ukraine forces regained the village of Krynky last month after they crossed the Dnipro, and have since come under relentless Russian attack.
Russia's defence ministry has meanwhile said its navy repelled a Ukrainian naval attack on occupied Crimea via the Black Sea.
Part of the peninsula, seized and then annexed by Russia in 2014, was placed under a state of emergency this week after a storm left five people dead. Coastal areas were worst hit, according to Russian-appointed leader Sergei Aksyonov.