Fog helps Russian forces push deeper into key Ukrainian city of Pokrovsk

This image of Russians riding into Pokrovsk in the fog appeared on social media on Monday

Thick fog has enabled Russian troops to move further into the key strategic city of Pokrovsk in eastern Ukraine.

Ukraine's 7th Airborne Assault Corps says weather conditions, particularly dense fog, have prompted Moscow to intensify its bid to get increasing numbers into the ruined city and then encircle Ukrainian forces.

Russian forces have spent more than a year trying to capture the city, and Ukrainian President Voloydymyr Zelensky says the fog has favoured Russian attacks and the situation remains difficult.

A video that has gone viral on social media shows Russian soldiers openly driving through a hazy road on civilian cars and motorbikes.

The BBC has verified the location where the video was filmed as the southern outskirts of the town on the Selidove-Pokrovsk highway.

For several days fog obscured visibility to carry out aerial reconnaissance, says a drone pilot from the "Shershni Dovbusha" unit of the 68th brigade with the call-sign "Goose".

That's why, he told the BBC, the Russians had even "dared" to launch assaults using a column of vehicles, which would normally have been wiped out immediately by Ukrainian drones.

The Ukrainian drone pilot told the BBC his unit had regularly detected and eliminated small Russian groups trying to advance on foot and on motor bikes. He added they were also involved in repelling the attack featured in the viral video, said to have been filmed on Sunday.

The convoy was partly destroyed, "Goose" claims, however weather conditions meant there was no video monitoring of the moment they repelled the attack so he was not sure if the entire group was hit.

The 7th Corps claims that there are now 300 Russian soldiers in Pokrovsk, although that was the figure initially shared by Zelensky last Wednesday. The video suggests those numbers have probably increased in that time.

Russian troops appear to be closing in on most areas of Pokrovsk, according to mapping by the Ukraine-based DeepState monitoring group. Some observers say that its fall is imminent.

Most parts of the city are now in a grey zone that neither side fully controls, says "Goose". "We might hold positions in one building, but the enemy can be in the next one. They're trying to get behind our backs," he says.

Moscow is trying to encircle Pokrovsk and neighbouring Myrnohrad in what is known as a "cauldron".

Even if the "lid" is not closed, Russians can constantly target all routes in and out of it using FPV drones.

To prevent such an encirclement, Ukrainian troops have pushed Russian troops back from Suvorove and Rodynske on the eastern part of the "cauldron", creating a bigger gap between Russian flanks.

Russian forces are trying to cut off logistical routes supporting Ukrainian troops in Pokrovsk.

They attack supply routes, not only remotely using drones and artillery but also by sending in soldiers on the ground, the Ukrainian drone pilot told the BBC.

This tactic is called infiltration and it has proved quite successful, says Ukrainian military analyst Kostyantyn Mashovets.

He argues that Russian forces have specifically targeted Ukrainian FPV pilots so they do not have sufficient resources to detect the movement of smaller Russian groups.

In an urban environment, Russian soldiers sometimes infiltrate by dressing up as locals or as Ukrainian military, says Mashovets. Their main goal is to cause chaos among Ukrainian defenders, which is then followed by a push from the main forces of the Russian army, he adds.

The Kremlin is also trying to push in other parts of the front line – in Kupyansk in the north-east and in Zapporizhzhya region in the south.

Viktor Tregubov, spokesperson of the Joint Forces Operation, denied Moscow's claim that they had managed to surround Kupyansk but admitted that Russian troops were present in the south of the town and the situation was difficult.