A set of mysterious symbols have emerged on various buildings in Kyiv, sparking fears that Russian saboteurs may be marking out targets for a major aerial assault, Daily Mail reported.

Images of the symbols circulated on social media after Ukraine's State Service of Special Communications and Information Protection (DSSZZI) posted a warning on social media encouraging residents to cover them up.

Red and orange crosshairs have been painted onto various structures in the capital, including several high-rise buildings, with certain symbols only visible under UV light, the report said.

"City officials are asking residents of high-rise buildings who have access to the roof to urgently check the rooftops for symbols," the post read.

"If any symbols are found, please cover them up with dirt or something else."

Russian forces disable 118 military facilities in Ukraine: Defense Ministry

Fears that the symbols could in fact be target indicators were confirmed over the weekend when Mayor of Kyiv Vitali Klitschko declared: "City officials are urging citizens to immediately report tagged locations, submit photos to law enforcement, and report suspects who may be involved in tagging."

"Labels are placed to adjust the fire of the occupying forces of the Russian Federation."

It comes amid rising concerns that Kyiv could soon come under heavy attack, after the Kremlin this morning warned civilians to leave the city via a "safe highway" to the southwest.

Russia used similar tactics during its intervention in Syria, in which military leaders told civilians to leave cities along a safe route before conducting heavy bombing campaigns while fighting alongside Bashar al-Assad.

Russian forces disable 118 military facilities in Ukraine: Defense Ministry

The use of target indicators (TIs) for aerial assaults was pioneered primarily by the RAF and the German Luftwaffe in World War II, Daily Mail reported.

Now, the Ukrainian military has reportedly seized several silent, light-emitting beacons from several positions around the capital, which are believed to be TIs for Russian aircraft or missiles.

These lights can be used as TIs to lead missiles to their targets with pinpoint accuracy and help them to avoid obstacles or enemy fire.

The painted crosshairs meanwhile represent a more old-fashioned approach to target indication - though they are less susceptible to sabotage, jamming and hacking unlike more technologically advanced methods, Daily Mail reported.

A video shared on Twitter purported to show one of the transmitting devices captured by Ukrainian forces, which flashed intermittently with a sharp green light.

(With inputs from IANS)