The UN’s nuclear watchdog says it will send a team to inspect two sites in Ukraine at the government’s request.

International Atomic Energy Agency (IAEA) inspectors will examine the sites for signs of “undeclared nuclear activities”, officials said.

The location of the facilities was not announced, but Director-General Rafael Grossi said that one of them was inspected last month.

It comes amid Russian accusations that Kyiv is preparing to use dirty bombs.

The devices contain radioactive material, such as uranium, which is scattered through the air when its conventional explosive detonates. They don’t need to contain highly refined radioactive material, as is used in a nuclear bomb, which makes them cheaper and easier to manoeuvre.

The IAEA said it received an invitation from the Ukrainian government to carry out “verification activities” at two unspecified locations, adding that the agency’s inspectors already visit both sites regularly.

The invitation appeared to be in response to Russia’s recent allegations that two institutes in Ukraine were involved in preparations to produce a dirty bomb. Moscow has not offered any evidence for the claim.

Russia’s state-run news agency, RIA Novosti, said it had identified two sites – the Eastern Mineral Enrichment Plant in central Dnipropetrovsk region and the Institute for Nuclear Research in Kyiv – as the locations central to the alleged Ukrainian operation.

Moscow is expected to repeat the allegation during a meeting of the UN’s Security Council on Tuesday. In a letter to UN Secretary-General Antonio Guterres, the Russian representative to the council, Vassily Nebenzia, said his country would “regard the use of the dirty bomb by the Kyiv regime as an act of nuclear terrorism”.

“Our Ministry of Defence has also received information that this provocation can be carried out with the support of Western countries,” Mr Nebenzia wrote in his letter.

Moscow’s allegations have been rejected by Ukraine and its Western allies. In a joint statement on Monday, the US, UK and French foreign ministers condemned the claims as “transparently false” and said the “world would see through any attempt to use this allegation as a pretext for escalation”.

Meanwhile, Ukrainian President Volodymyr Zelensky said the Russian allegations were clear signs that it was planning it own attack.

Speaking from Kyiv during his nightly address on Monday, Mr Zelensky said “if Russia calls and says that Ukraine is allegedly preparing something, it means one thing: Russia has already prepared all this”.

Western intelligence officials have been keen to stress that there is no indication that Russia is preparing to use so-called dirty bombs or other nuclear devices.

The Russian claims come as Ukrainian forces continue to gain ground in the southern Kherson region. Kyiv’s forces launched a counter-attack in the region in August and its forces have slowly moved towards the regional capital of Kherson city.

In recent days, Moscow-installed officials have fled the city and urged civilians to evacuate over the Dnieper river into Russian controlled territory.

But Ukraine’s military intelligence chief, Kyrylo Budanov, warned state media that Russian troops in the region were preparing the defend the city rather than retreat.

“They are creating the illusion that all is lost. Yet at the same time they are moving new military units in and preparing to defend the streets of Kherson,” Mr Budanov said.

Regional authorities have said that some men who chose to remain behind in the city would have the option of joining local militias to defend it, raising fears that Moscow could force men into military formations. Such actions would constitute war crimes under the Geneva convention.

Kherson is the only major Ukrainian city that Russian forces have managed to capture during its invasion, and its only major foothold west of the River Dnieper.