Officials at the UK defence ministry made the assessment on Wednesday.
They noted that since December 29, 2023, Russia had stepped up "the intensity of its long-range operations against Ukraine."
The air attacks, using air-launched cruise missiles and ballistic missiles, among other weapons, "likely primarily targeted Ukraine's defence industry," British officials assessed.
This is in contrast to Russia's long-range strikes the previous winter, which were aimed at Ukraine's energy infrastructure, the UK defence ministry added.
Moscow's planners have likely changed their approach because they have recognised the "growing importance of relative defence industrial capacity" for the outcome of the war, British officials said.
The UK defence ministry added that Russia is preparing for a "long war."
Russia on Tuesday morning launched an air attack on Ukraine's two biggest cities, Kyiv and Kharkiv, killing at least five people, according to Ukrainian officials.
On Friday, Russia launched the largest attack of the war, killing at least 39 Ukrainian civilians, the Reuters news agency reported.
More Russian air assaults on Ukraine followed on Sunday and on New Year's Day, according to news outlets.
Ukraine's President Volodymyr Zelensky said that between December 29 and January 2, Russia fired at least 500 missiles and unmanned aerial vehicles against his country.
Wednesday is day 679 of Russia’s war on Ukraine.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
(pm)
Source: UK Ministry of Defence, The Telegraph