Kremlin spokesman Dmitry Peskov has denied that Russia’s invasion of Ukraine has stalled.

Asked on CNN what Russian President Vladimir Putin has achieved in Ukraine, he said: “Well, first of all not yet. He hasn’t achieved yet.”

But he insisted the military operation was going “strictly in accordance with the plans and purposes that were established beforehand”.

Mr Peskov reiterated that Mr Putin’s main goals were to “get rid of the military potential of Ukraine” and “ensure that Ukraine changes from an anti-Russian centre to a neutral country”.

Meanwhile, Ukrainian President Volodymyr Zelensky said Russian forces not only blocked a humanitarian convoy trying to reach besieged Mariupol with desperately needed supplies on Tuesday, but took captive some of the rescue workers and bus drivers.

He said the Russians had agreed to the route ahead of time.

“We are trying to organise stable humanitarian corridors for Mariupol residents, but almost all of our attempts, unfortunately, are foiled by the Russian occupiers, by shelling, or deliberate terror,” Mr Zelensky said.

Elsewhere, Russian military forces destroyed a new laboratory at the Chernobyl nuclear power plant that, among other things, works to improve management of radioactive waste, the Ukrainian state agency responsible for the Chernobyl exclusion zone said on Tuesday.

The Russian military seized the decommissioned plant at the beginning of the war. The exclusion zone is the contaminated area around the plant, site of the world’s worst nuclear meltdown in 1986.

The state agency said the laboratory, built at a cost of six million euros (£4.9 million) with support from the European Commission, opened in 2015.

The laboratory contained “highly active samples and samples of radionuclides that are now in the hands of the enemy, which we hope will harm itself and not the civilised world,” the agency said in its statement.

In another worrying development, Ukraine’s nuclear regulatory agency said on Monday that radiation monitors around the plant had stopped working.