Russian authorities have reported an explosion in the city of Belgorod near the border with Ukraine, saying the blast left a massive crater in the city centre.
They have since said a fighter aircraft lost ammunition over the city.
"An abnormal descent of aviation ammunition has occurred," the defence ministry said in a statement carried by Russian news agencies.
Vyacheslav Gladkov, governor of the Belgorod region, said that there are "no victims" after the blast.
He added that a "huge" crater some 20 metres wide had appeared in the city centre.
Belgorod mayor Valentin Demidov arrived at the scene and posted pictures of damage on Telegram.
One picture showed him speaking to a local resident in what appeared to be her damaged apartment.
Neither the governor nor the mayor said what caused the explosion, but Mr Gladkov said that the blast had sent a massive wave that shattered windows in an apartment building, damaged several cars and downed power line poles.
Mr Demidov said that residents of the buildings damaged in the blast could be temporarily moved to hotels.
The Belgorod region, including the city of the same name, has been repeatedly hit by shelling since President Vladimir Putin sent troops to Ukraine in February 2022.
In January, Mr Gladkov told Mr Putin that 25 people had been killed and more than 90 injured in the region since the start of the offensive.
Ukraine appeals to NATO chief
Ukrainian President Volodymyr Zelensky has told visiting NATO chief Jens Stoltenberg it was time for the military alliance to offer his country membership and that Kyiv needed more weapons to fight Russia.
Mr Zelensky made his comments at a joint news conference after talks with Mr Stoltenberg, who offered NATO's solidarity with Ukraine on his first trip to Kyiv since Russia's full-scale invasion nearly 14 months ago.
The NATO secretary-general's visit was likely to irk the Kremlin, which said earlier that one of the main goals of its "special military operation" in Ukraine was to prevent it joining what Moscow regards as a hostile bloc.
Mr Zelensky said he believed a NATO Summit in Vilnius in July could become "historic" and that he had been invited to attend.
"I am grateful for the invitation to visit the summit, but it is also important for Ukraine to receive the corresponding invitation," Mr Zelensky said.
"There is no objective barrier to the political decision to invite Ukraine into the alliance and now, when most people in NATO countries and the majority of Ukrainians support NATO accession, is the time for the corresponding decisions."
NATO has supported Ukraine throughout the war, with member states supplying it with weapons, but Mr Zelensky said more were needed.
All delays in receiving more weapons caused deaths in Ukraine, he said.
Mr Stoltenberg said Ukraine's rightful place was in the North Atlantic Treaty Organization, and that membership and security guarantees for Ukraine would be high on the agenda of the alliance's July summit.
"Mr President, I am here today with a simple message: NATO stands with Ukraine," he said.
"NATO stands with you today, tomorrow and for as long as it takes."
Ukraine announced a bid for fast-track membership of NATO last September after the Kremlin said it had annexed four Ukrainian regions that its troops have partially occupied.
The Kremlin reiterated to reporters on a conference call that Moscow opposed NATO admitting Ukraine, a former Soviet republic.
"...otherwise it will present a serious, significant danger to the security of our country," Kremlin spokesman Dmitry Peskov said.
Mr Stoltenberg's visit to Kyiv comes at a vital juncture in Russia's almost 14-month-old invasion which has killed thousands, uprooted millions, destroyed cities and devastated the Ukrainian economy.
After weathering a Russian winter and spring offensive that has made only small advances in the east, Ukraine now hopes to retake land in its south and east in a counteroffensive in the coming weeks or months.
Mr Stoltenberg also began his trip a day before NATO defence officials discuss new military supplies for Ukraine at their latest meeting at the Ramstein Air Base in Germany.
Denmark and the Netherlands announced they would jointly donate 14 Leopard 2 tanks.
On Wednesday, Washington announced $325 million in new military aid, including ammunition for High Mobility Artillery Rocket Systems (HIMARS), advanced missiles and anti-tank mines.
Russian recruitment drive seeks 'real' men
Meanwhile, the Russian military has launched a video campaign to lure more professional soldiers to fight in Ukraine which challenges those interested to show they are "a real man" and swap what it casts as hum-drum civilian life for the battlefield.
The ad, set to stirring music, follows a report from British military intelligence and Russian media reports that suggest Moscow is seeking to recruit up to 400,000 professional soldiers - on a volunteer basis - to bolster its forces in Ukraine.
The ad has so far been released on major Russian social networking sites.
Russia, which says it is prosecuting what it calls "a special military operation," does not disclose full casualty figures.
But up to 43,000 Russians have been killed in the war so far, according to a recently leaked estimate from the US Defence Intelligence Agency.
It estimated up to 17,500 Ukrainians had been killed too.
The ad, which invites men to sign a contract with the Russian Defence Ministry for a salary starting at 204,000 roubles (€2,278) a month, shows a man in supermarket dressed in military uniform holding a heavy machine gun.
He is then shown in the uniform of a security guard with the question: "Is this the kind of defender you dreamt of becoming?"
Next in the video, a man is walking through the fog with other soldiers on what looks like a battlefield. He is then shown as a gym instructor helping a client lift weights.
"Is this really where your strength lies?" the video asks, before cutting to a taxi driver taking a client's fare who then transforms into a soldier on the battlefield.
"You're a real man. Be one," says the ad.
