Russian troops are making a concerted push in eastern Ukraine and have gained a foothold in the strategic hub of Pokrovsk, Ukrainian President Volodymyr Zelensky says.

Moscow's soldiers outnumber Kyiv's 8-1 in the area and Ukraine cannot match that, Zelensky added while insisting Russia had not yet achieved the planned result.

Russia has been trying to capture Pokrovsk for two years. The key supply and transport hub provides supplies and reinforcements to the eastern front - and it would get Moscow closer to occupying the entirety of the Donetsk region.

It would also put towns of the heavily fortified fortress belt - Kramatorsk, Slovyansk, Kostyantynivka and Druzhkivka - within easier reach of Moscow.

Zelensky said drone imagery showed that around 200 Russian soldiers were inside Pokrovsk.

Describing the situation as difficult, he said earlier that there was widespread fierce fighting and sabotage groups had entered the town.

However, he rejected reports by Russia's Chief of General Staff, Gen Valery Gerasimov, that Ukrainian troops had been completely surrounded.

In an update on Tuesday, Russia's defence ministry said its forces had encircled Ukrainian troops around the main railway station and cleared the city's Troyanda district of Ukrainian forces.

One soldier from Ukraine's 155th Brigade, Artem Pribylnov, rejected the notion that Ukrainian troops had been encircled in a cauldron at Pokrovsk.

But the war has changed and it's very technological now, he said.

In previous assaults, there had been a path out of the cauldron that troops could drive in and out of, he said, but now drones controlled access points, which made it extremely dangerous.

According to Capt Hryhoriy Shapoval, spokesperson of Ukraine's East operational group, 79 attacks had been repelled near Pokrovsk since Monday - almost a third of the total 218 assaults recorded across the entire front line.

He added that Kyiv's troops normally used drones to counter the Russians' advance but foggy and rainy weather conditions had made it harder to detect and destroy infantry troops.

The situation in and around Pokrovsk exemplifies the high cost of shifting the front line forward, even just by a few metres. Russia's full-scale invasion in February 2022 is almost into its fifth year. Moscow's troops currently occupy about 20% of Ukrainian territory.

Kyiv's defence capabilities are shrinking, and Zelensky has said Ukraine needs financial support from its European allies to continue fighting Russian forces for another two or three years. European leaders have so far failed to divert €140bn worth of Russian frozen assets to Ukraine, which was blocked by Belgium at an EU summit last week.

The Ukrainian president also expressed hope for a meeting between US President Donald Trump and Chinese leader Xi Jinping, hoping it might lead to a decision by China to cut support for Russia.