• Analysts have long said Russia was keeping missiles and bombs in reserve for winter.

• Winter is here — and a Russian barrage has begun right on cue.

• The UK MOD said Russia's heavy bomber fleet has been active. Its target is likely Ukraine's energy network.

Russia appears to have started a major bombing campaign on Ukraine after holding back for months to build its stockpiles.

The UK Ministry of Defence said on Sunday that a cruise missile attack last Thursday was "probably the start of a more concerted campaign by Russia aimed at degrading Ukraine's energy infrastructure."

The missiles "were highly likely AS-23a KODIAK," Russia's premier air-launched cruise missile, the MOD said.

"Russia has almost certainly been stockpiling these missiles for use in the winter campaign," it said.

Its assessment came after a previous warning in October that a slowdown in Russian cruise-missile attacks was probably a sign of worse to come.

It was pulling back to to replenish its missile stockpile to be ready for winter, the MOD said.

Ukraine's energy network is a tempting target in the winter months, when it is most needed to stave off the country's freezing weather.

Ukraine and its allies expected Russia to repeat the tactic that it used last winter.

Russia then frequently knocked out Ukrainian power, leaving Ukraine scrambling to repair the damage. The strikes also killed civilians, and led to Ukraine setting up heating points to try and keep other civilians warm.

Russia in its attack last week used its heavy bomber fleet for the first time since September 21 to conduct "a major wave of strikes towards Kyiv and central Ukraine," the UK MOD said.

It said the Tu-95 BEAR H bomber probably featured, and that they likely launched at least 16 cruise missiles from over the Caspian Sea.

At least one Ukrainian civilian was killed, according to Ukrainian media.

Ukraine isn't powerless against the strikes, though — the UK MOD update said most of the missiles appeared to be intercepted by Ukraine's air defense, citing initial reports.