Kyiv's military administration says an air raid alert was activated but "air defence was not in operation", while the Ukrainian air force said a satellite plunging from orbit or a meteorite could be responsible - but NASA has denied any involvement.

A mysterious flash of light that lit up the skies over Kyiv sparked alarm, confusion and speculation as to what may have caused it.

Four short video clips posted to a Telegram channel by journalist and blogger Anatolii Sharii showed the sky over the  Ukrainian  capital suddenly illuminated.

Sergiy Popko, head of the city's military administration described it as a "bright glow" on the messaging app.

He said an air raid alert was activated but "air defence was not in operation".

In one clip, a flaming object appeared to be crashing to the ground.

The Ukrainian air force, which aims to bring down missiles and drones fired by  Russia , said a satellite plunging from orbit or a meteorite could be responsible.

"At the current time there is no risk of the enemy using air attack weapons," it said.

Minutes earlier, presidential adviser Andriy Yermak had posted an emoji of a UFO.

Social media users reacted with memes as they speculated about the cause of the glow.

"Please do not use official air force symbols to create memes for the enemy to enjoy!" the Ukrainian air force said in a message.

The Austrian ambassador to Kyiv posted a video of the incident, and joked about others on Twitter suggesting it was an alien spacecraft.

The city's military administration, citing what it called preliminary information, said it was a crashing  NASA  satellite.

The US space agency denied this - and said there appeared to be some confusion over its announcement earlier this week that it was  bringing a retired satellite out of orbit .

It said the satellite - sent into orbit in 2002 to study the sun - was still in orbit at the time of the flash.

On Monday, NASA said the 300kg defunct spacecraft, known as Rhessi, would plummet through the atmosphere on Wednesday night.

Most of it would burn up, but some parts were expected to fall to Earth.