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, just over 30 kilometres from the Russian border, were defiant despite the threat.
Mr Putin raised the possibility of setting up a buffer zone during a speech after winning re-election yesterday, a move the Kremlin said would be the only way to protect Russia from Ukrainian attacks.
In a call with reporters, Kremlin spokesman Dmitry Peskov said: "Against the backdrop of (Ukrainian) drone attacks and the shelling of our territory: public facilities, residential buildings, measures must be taken to secure these territories.
"They can only be secured by creating some kind of buffer zone so that any means that the enemy uses to strike us are out of range."
"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.
Mr 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.
"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.
China considers taking part in Swiss Ukraine peace talks, ambassador says
Meanwhile, China will consider taking part in a peace conference aimed at ending the war in Ukraine which neutral Switzerland plans to host in the coming months, the Asian country's ambassador to Bern was quoted as saying.
Wang Shihting, China's ambassador to Switzerland, said in an interview with the Neue Zuercher Zeitung that all parties should work to end the war, which began over two years ago.
"The crisis must be prevented from getting even worse, or even getting out of control," he said. "We are closely following the Ukraine conference that Switzerland will host, and are examining the possibility of taking part."
The Swiss government has said it aims to hold the peace conference by this summer after the idea was floated in January.
Russia, which invaded Ukraine in February 2022, then called the peace conference plan "pointless" and indicated it was doomed to fail without Moscow's participation.
Last month, Swiss President Viola Amherd said it was doubtful that Russia would take part at the outset of talks.
In the interview, Wang stressed China had put forward a strategy for a political end to the conflict.
"The territorial sovereignty of all countries must be respected, and the UN Charter must be adhered to," he said.
"We should support Russia and Ukraine resuming direct dialogue as quickly as possible so that the situation can be gradually de-escalated," Mr Wang said.
Meanwhile, Ukrainian air defence systems shot down 17 out of 22 Russian drones over nine Ukrainian regions in an attack that caused a fire in a residential building in the early hours of today, officials said.
No casualties were reported from the fire in the central city of Kryvyi Rih where emergency services were able to evacuate residents and disable a drone's payload before it blew up, local authorities said.
In central Kirovohrad region, the attack damaged private industrial facilities and nearby residential buildings, but there were no reported injuries, Kirovohrad governor Andriy Raykovych said on the Telegram messenger.
Russia also launched seven missiles at targets in Ukraine overnight, the air force said in a statement on Telegram.
An overnight missile strike on eastern Kharkiv region damaged a fire station and injured one person, the state emergency service said.
It was not immediately clear what happened to the missiles and the drones that were not destroyed.
