This week Ukrainian forces began a long-awaited counteroffensive aiming to retake the southern province of Kherson.
President Volodymyr Zelensky’s advisors have said their army has broken through Russian defences in several areas of the frontline near Kherson city.
The Russian military has been “dismayed” by its command centres in Ukraine being hit with long-range strikes, Western officials said on Friday.
“Ukraine's use of these long range strikes has achieved a substantial effect against Russia and all over the over Kherson,” they said.
“It is forcing Russia to adjust its positioning, adjust its tactics and has caused considerable dismay within the Russian armed forces as they struggle to adapt to Ukraine's precision, long range strike capability.”
Russia also has huge challenges replenishing its munitions supplies and has been “scraping around trying to bring back into service equipment which had previously been mothballed”, the officials added.
Earlier this week, Ukraine’s operational command in the South said its forces had destroyed a pontoon bridge near the town of Daryivky in the Kherson region, which was being used by Russian troops to bring in equipment and ammunition.
The progress of the counterattack is expected to be slow.
The general staff of Ukraine’s armed forces also reported on Thursday fighting near the Zaporizhzhia nuclear power plant and further afield along front lines in the east and south.
Western officials vowed on Friday that they will “absolutely guarantee” the continued supply of munitions and materials to Ukraine as it continues the slow counteroffensive against Putin’s army.
National Security Adviser Sir Stephen Lovegrove said: "It’s been more than six months since Putin launched his unprovoked, illegal war bringing untold suffering to the innocent people of Ukraine and there is increasing evidence of atrocities committed by Russian forces.
“Putin's invasion has hurt people across the globe, causing price rises and food insecurity, including for many who were already vulnerable, as well as the desperate bloodshed.
"Ukraine’s resistance has inspired the world and shown huge courage in the face of brutality. Now that courageous resistance has stalled the Russian advance and demonstrated the determination of the Ukrainian people and Armed Forces to retake their sovereign territory.
"The risks around this terrible conflict continue as Putin finds he can’t make progress, his forces suffer heavy losses, and sanctions continue to degrade his war machine and take money out of the pockets of Russia's richest people.
“At the same time Russia is trying and failing to impose a veneer of legitimacy on the areas it temporarily controls, including through plans for staged sham referenda.
“It will not succeed. The UK and our allies will continue to provide humanitarian, economic and military assistance.
“Our support for Ukraine and its people will not waver."