The photo was first uploaded by the Slovenian Radioactive Waste Agency in 2010.
Russia's foreign ministry has used an outdated photo online to claim that Ukraine is preparing a "dirty bomb".
The image posted on Twitter dates back to at least 2010 and was first posted by the Slovenian Radioactive Waste Agency (ARAO).
Moscow claimed that the photo showed evidence that "two organisations [in] Ukraine have been directly ordered to create the so-called dirty bomb".
"The works are at their concluding stage," the foreign ministry claimed on Twitter, quoting the defence ministry.
Ukraine and its Western allies have denounced the allegations as "absurd" and "dangerous" and have suggested that Russia was instead preparing to escalate the war.
On Wednesday, the Slovenian government confirmed that the photo used by Russia's foreign ministry belonged to the ARAO and was published without their knowledge.
According to Moscow, the photo shows bags of radioactive materials that might be used in a "dirty bomb".
But Slovenia's government said on Twitter that the image did not show "any radioactive sources listed [by Moscow]".
"It was used for professional presentations for the general and interested public as explanatory material. The photo shows smoke detectors that are subject to general use," it said.
"Radioactive waste in Slovenia is stored safely and is under supervision," added ARAO director Sandi Viršek. "It is not used for [the] making of any dirty bombs."
Dragan Barbutovski, an adviser to Slovenian Prime Minister Robert Golob, also told AFP that the ARAO photo was "misused".
The tweet by Russia's foreign ministry included images of a nuclear power plant, a radioactive waste storage site, and "scientific research reactors".
Online analysis shows that one of the images, of a supposed "scientific research reactor", is actually a stock photo of the Beloyarsk nuclear power plant in Russia, more than 1,000 kilometres from the Ukrainian border.