Ukraine's air raid alert app was apparently hacked on Sunday and for a short time said the capital Kyiv was subject to a radiation threat, the Ukrainian Air Force has said.

The Air Force message on Telegram read: "The Air Alarm application has probably been subjected to hostile interference. There is no radiation threat! Stay calm and follow our updates on our channel."

The Ukrainian Central Intelligence Agency said on Telegram that there had been a failure in the app, and urged people to use other sources of information to clarify the situation regarding the threat of air strikes.

The messages, in Ukrainian, started at approximately 22:47 (20:47 GMT), with the first reading: "Radiation threat. Radiation threat declared in Kyiv."

The next alert, written in Russian, came at 22:48, which read: "Hi! There will be a nuclear alert across Ukraine. Don't worry, it's Oreshnik flying".

A third alert, at 22:49, again in Ukrainian, said "Chemical threat. There is a threat of a chemical attack on Kyiv. Don't go outside."