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A mysterious flash which lit up skies over Ukraine's capital on Wednesday night generated much speculation.

Officials in Kyiv initially suspected it was a Nasa satellite falling to Earth but the US space agency told the ����ý it was still in orbit.

Ukrainian space officials said later the flash had probably come from a meteor entering the atmosphere.

The air force was confident it was not a Russian air attack - an event all too familiar since the invasion last year.

The bright glow was observed in the sky over the capital around 22:00 local time (19:00 GMT).

An air raid alert was activated but "air defence was not in operation", the head of Kyiv's military administration, Serhiy Popko, said on Telegram.

Mr Popko suggested it was caused by a Nasa space satellite falling to Earth, referring to a retired 300kg (660lb) spacecraft that the space agency announced was set to re-enter the atmosphere on Wednesday.

The RHESSI satellite, used to observe solar flares, was launched into low Earth orbit in 2002 and decommissioned in 2018, Nasa said.

But Rob Margetta from Nasa's office of communications told the ����ý that the satellite was still in orbit at the time the flash was observed, and was due to re-enter Earth's atmosphere during the night.

Satellite-tracking website Satflare indicated that RHESSI was nowhere near Ukraine at the time.

Ukrainian social media has been awash with theories and memes about what the flash could have been, with a popular theme being that it was caused by aliens.

But air force spokesman Yuri Ihnat told Ukrainian TV that the flash had also been seen over neighbouring Belarus to the north and Ukraine's space agency said it was probably related to a cosmic body entering the dense layers of the atmosphere.

Kyiv officials said it was up to experts to establish what it was but what was most important was the city's security.