A senior Ukrainian official said Russian President Vladimir Putin's idea of creating a buffer zone inside Ukrainian territory was a clear indication that Moscow planned to escalate its war in neighbouring Ukraine.
But residents of Ukraine's northeastern city of Kharkiv, less than 20 miles from the Russian border, were defiant despite the threat.
Putin raised the possibility of setting up a buffer zone during a speech after winning re-election on Sunday, a move the Kremlin said would be the only way to protect Russia from Ukrainian attacks.
"This is ... a direct manifest statement that the war will only escalate," presidential aide Mykhailo Podolyak told Reuters in a written statement.
"All this is direct evidence that the Russian Federation is not ready to live in modern social and political relations, taking into account the absolute sovereign rights of other countries," he said.
Putin made the comment after winning a fifth term in the Kremlin at a three-day election decried as a sham by the West.
The Kremlin leader did not provide details, but said the buffer zone may have to be big enough to stop what he said were foreign-made weapons striking Russian territory.
He made the remark after being asked whether he thought it necessary for Russia to take Ukraine's Kharkiv region, which borders Belgorod, a Russian province that has come under regular attack from Kyiv's forces since 2022.
Residents of Kharkiv, the region's eponymous capital city, expressed defiance when asked about the Russian leader's words on Monday.
"I think he (Putin) will choke on his words. Kharkiv is never going to be a grey zone. Kharkiv is and will be Ukraine. Let him choke," said resident Antonina Khrypushkina.
Russia has been bombarding Kharkiv and the surrounding region with missiles and drones almost every day in recent months.
Roman Artiukh, a soldier serving in Ukraine's armed forces, quipped that it was Kyiv that needed to create a security zone inside Russia.
Ukraine has previously said that it only uses its own weapons to hit Russian territory. Some of its key allies, such as the US, have provided weapons on the condition they are not used inside Russia.
Kyiv stepped up its long-range drone strikes on oil refineries in Russia last week and paramilitary groups also staged cross-border attacks from Ukraine into western Russia.
