The war in Ukraine will enter a new phase, British military intelligence chiefs said this morning.

Russian forces are "almost certainly" massing in the south in preparation for a counterattack from Ukraine, the Ministry of Defense (MoD) warned,

reports .

Long convoys of military trucks, tanks and towed artillery are moving southwest away from the Donbass region in eastern Ukraine, the Defense Ministry said on Twitter in an intelligence update.

"Russia's war against Ukraine is about to enter a new phase, with the fiercest fighting shifting to a roughly 350 km front line that stretches southwest from near Zaporizhzhia to Kherson, parallel to the Dnieper River," he wrote in Twitter.

The battalion's tactical groups – consisting of 800 to 1,000 troops – have been deployed in annexed Crimea and are expected to support Russian troops in Kherson, according to the Defense Ministry update.

Latest Defense Intelligence update on the situation in Ukraine – August 6, 2022

Find out more about the UK government's response: https://t.co/ipwkuIN1lV

🇺🇦 #StandWithUkraine 🇺🇦 pic.twitter.com/cyB1fVrATh

— Ministry of Defense 🇬🇧 (@DefenceHQ) August 6, 2022

The equipment is also believed to have been moved from mainland Russia and Moscow-occupied areas – including Melitopol, Berdiansk and Mariupol – via the Kerch bridge into Crimea.

Kiev is focusing on targeting bridges, ammunition depots and rail links with increasing frequency in the southern regions.

Key to this strategy is the significant rail spur linking Kherson to Crimea, with a combination of “block, damage, deny, destroy and disrupt” effects to be deployed in the hope of hampering Russia's ability to logistically resupply.

The Defense Ministry's warning comes hours after Kiev and the Kremlin blamed each other for the bombing of Europe's largest nuclear power plant in Zaporizhzhia.

The factory was seized by Russian forces in March, but continues to be run by Ukrainian technicians.

Meanwhile, the southern frontline city of Mykolaiv imposed an unusually long curfew from late Friday to early Monday morning as authorities try to catch people collaborating with Russian rivals, the region's governor said.

Some 131 deaths, including a child, have been recorded in the southern port city, located on the Black Sea, since the invasion began.

Seven children are among 590 other people injured in the attacks in Mykolaiv.

Ukraine's foreign ministry said the consequences of striking an operating reactor are "equivalent to using an atomic bomb" - after President Volodymyr Zelenskyy called for new sanctions on Russia's nuclear industry.

But the Russian defense ministry hit back, claiming it was luck that a radiation leak was avoided.

Earlier this week, UN Secretary-General Antonio Guterres warned humanity is "one misunderstanding away from nuclear annihilation" - citing Russia's invasion of Ukraine amid crises "with angsty nuclear undertones".