Six Russian balloons were spotted over Kyiv and most were shot down after being engaged by air defenses, the Ukrainian capital's military administration said Wednesday.

It said the balloons may have been carrying corner reflectors and reconnaissance equipment but did not specify when they flew over the capital, although air alerts were issued in Kyiv on Wednesday.

"According to information that is now being clarified, these were balloons that move in the air under the propulsion of wind," the military administration wrote on the Telegram messaging app.

"The purpose of launching the balloons was possibly to detect and exhaust our air defenses."

Shortly before the announcement, Ukrainian air force spokesperson Yuriy Ihnat said Russia, which invaded Ukraine in February last year, could be using balloons in a new drive to preserve its stocks of reconnaissance drones.

"Reconnaissance drones like the Orlan-10 are now being used more sparingly (by Russia), and they thought 'Why don't we use these balloons?' So they are using them," Ihnat told Ukrainian television.

He later confirmed that air raid sirens had blared in the capital on Wednesday because of balloons flying overhead.

Russia did not immediately comment on the reports of balloons over Kyiv.