A flash in the sky over Ukraine has sparked confusion with authorities claiming it was caused by Nasa.
The "bright glow" was seen over Kyiv at around 10pm local time, according to the capital's military adviser Sergiy Popko.
Officials said it was caused by a NASA satellite re-entering the atmosphere, while the US space agency denied involvement.
An air raid alert was activated but "air defence was not in operation," Popko explained.
The Ukrainian air force later said the flash was "related to the fall of a satellite or meteorite".
But a NASA spokesperson said the satellite in question was "still in orbit."
The flash was seen in the sky over Kyiv at around 10pm local time.
Space officials in Ukraine later said that the flash had likely come from a meteorite entering the atmosphere.
The air force was confident it was not a Russian air attack.
Earlier this week, NASA said that its retired 660lb RHESSI satellite would reenter the atmosphere on Wednesday.
It expected most of the aircraft, used to observe solar flares, to burn up as it travelled through the atmosphere with some parts surviving the journey.
A spokesperson said: "The risk of harm coming to anyone on Earth is low – approximately 1 in 2,467."
However, its office of communications told the BBC that RHESSI was still in orbit at the time of the flash in Ukraine.
It added that the US defence department and the American space agency was still tracking it.
Meanwhile data from Satflare satellite-tracking website suggests that it was nowhere near Ukraine at the time.
People have flocked to social media to share their theories of what could be behind the flash.
One popular theme is that it was caused by aliens.
But other repots show that the flash was also seen elsewhere including Belarus, to the north of Ukraine.
Air force spokesperson Yuri Ihnat told Ukrainian TV that it was likely related to a cosmic body entering the dense layers of the atmosphere.
Officials in Kyiv said the identification of the flash would be confirmed by experts while the city's security is the most important thing.