The European Union has agreed to launch a stockpiling operation to boost its defences against chemical, nuclear and biological incidents amid concerns over the conflict in Ukraine, according to EU documents and people familiar with the matter.

The stockpiling of protective gear and medicines is expected to last weeks, potentially a few months, and is meant to expand reserves available to the EU population and partner countries, including Ukraine.

The supplies will also include decontamination equipment, gloves, masks and other material for chemical, biological, radiological and nuclear defence (CBRN), two people familiar with the matter told Reuters on Friday.

The European Commission declined to comment.

Concerns about nuclear incidents in Ukraine partly prompted the move, according to the minutes of two meetings of EU health experts in March made public this week.

Russian troops took over the Zaporizhzhia nuclear site, the largest in Ukraine, in the early stages of the invasion, which the Kremlin calls a special operation.

"Nuclear sites are operated by highly trained and qualified staff, which is difficult within the current conflict situation, especially when taken over by military forces," EU officials said with reference to the takeover, the minutes of the March 16 meeting showed.

Russia has repeatedly raised the prospect of using nuclear weapons as it struggles to overcome Ukraine's military during the month-old war.

Western officials have also voiced fears that Russia may use chemical and biological weapons in Ukraine, with risks of spillover effects beyond the country.

France, which holds the rotating presidency of the EU, called in the internal meetings for a bloc-wide plan to distribute potassium iodide tablets, which are used to protect people exposed to nuclear radiation.

French officials in Brussels had no immediate comment.

About 20 EU states already have stockpiles of iodine pills, according to a survey conducted by the EU Commission and shared in the March 16 meeting of health experts.

Many of these national reserves predated the Ukraine crisis.

Lithuania, for instance, has distributed iodine pills since last year as a precautionary measure after the opening of the Astravets nuclear power plant in neighbouring Belarus.

It extended the practice last month to ensure full coverage of the eligible population.

Sweden has had reserves of potassium iodide for decades, Jan Johansson, government expert at the Swedish Radiation Safety Authority, told Reuters.

These pills are distributed to - or stocked for - people who live close to nuclear plants, and the government has decided to increase the number of eligible people, including those who live up to 100 km from nuclear sites, from next summer.

Johansson said that had nothing to do with the Ukraine war.

"We assess that an accident in Ukraine cannot have any impact on Sweden that would justify taking potassium iodide tablets. The distance is just too far," he said.

CBRN DEFENCE

The sources did not clarify which medicines the EU is planning to stockpile as CBRN defence.

Together with the United States, Russia is the only country known to have the smallpox virus, infectious disease expert Antonino Di Caro told Reuters.

"This does not mean they will use it," Di Caro said, underlining that using viruses or bacteria as biological weapons also entails huge risks for those who deploy them.

The smallpox virus has been considered eradicated since 1980 after a global vaccination campaign. If it resurfaced, younger people would not be protected against it unless quickly vaccinated.

Di Caro, who until February led the section on biological weapons of the EU project TERROR for preparedness and response planning to biological and chemical attacks, said it was not clear how big the bloc's stockpile of smallpox vaccines is.

He said the risk of an attack with toxins such as botulinum could be higher as they are easier for attackers to control.