“I have no doubt that it was not our missile,” he said, according to the Interfax Ukraine news agency.
Nato is conducting an investigation into the apparent strike on the village of Przewodow - which killed two people - but on Wednesday its general-secretary Jens Stoltenberg said the blast was likely to have been caused by a stray Ukrainian air defence missile.
Within hours of the incident, Mr Zelensky had blamed it on “Russian missile terror”, and Kyiv did not appear ready on Wednesday to concede its own missile may have been involved.
Russia was quick to deny involvement. Its ministry of defence described claims of Russian involvement as “a deliberate provocation aimed at escalating the situation”.
The Kremlin said on Wednesday that some countries had made “baseless statements” about the incident, after having accused Poland of an “absolutely hysterical” reaction on Tuesday, but that Washington had been comparatively restrained.
However the Ukrainian claims against Russia continued on Wednesday , with a senior defence official alleging Kyiv has evidence of a “Russian trace” in the explosion, without giving any details.
Oleksiy Danilov, secretary of the National Security and Defence Council of Ukraine, said Ukraine wanted a joint study of the incident with its partners. He said the country also wants to see the information that provided the basis for its allies’ conclusions that a Ukrainian missile was probably behind the blast.
Kyiv is “completely open to a comprehensive study of the situation”, he wrote on the council’s official Facebook page.
Mr Stoltenberg said that, while it appeared the explosion was caused by a Ukrainian missile, Moscow, the blame for it ultimately lay with Moscow not Kyiv.
“This is not Ukraine’s fault. Russia bears ultimate responsibility as it continues its illegal war against Ukraine,” he told reporters in Brussels.
The incident occurred while Russia was firing scores of missiles at cities across Ukraine, in what Kyiv said was the most intense wave of strikes in the nine-month war.