At 22:49, a fourth alert stated there was a "Street fighting threat. Street fighting is taking place in Kyiv. Don't go outside."

At 23:53 a series of all clear messages were then delivered to users' phones, which were connected to each of the previous Kyivalerts, individually declaring each threat clear.

In a separate post on Telegram, the Ukrainian Central Intelligence Agency said that due to the Air Alert application, the Radiation Hazard signal was played on loudspeaker devices in the Lviv region, and added there was no threat of radiation hazard.

If the alert app is not working, Ukraine's Centre for Countering Disinformation advises the public to turn on notifications on their smartphones, pay attention to sirens, and to only read official sources

Several governors of other regions also posted on Telegram that the app had apparently been hacked and there was no local threat.

"Everything is calm in the region for now," said Svitlana Onyshchuk, the governor of the Ivano-Frankivsk Oblast. The app had reported a red-level air raid alert for the oblast in Ukraine's east, between 22:50 and 23:57.

The governor of Vinnytsia oblast, Natalya Zabolotna said there had been a cyber-attack on the Air Alert app and posted a warning on Telegram not to click on the link in the message, which could be a phishing attempt.

The Air Alert app is supported by the Ministry of Digital Transformation of Ukraine, and informs users instantly about the beginning and end of defence alerts. The ministry had earlier said the app was temporarily disabled for maintenance after it had "apparently been compromised". It urged residents to turn on their smartphones' emergency notifications so they could receive state-issued distress signals.

The alerts occurred just minutes before the end of a localised ceasefire in Ukraine's front-line Kherson region, which was implemented last Tuesday and officially ended at 23:00 Sunday.

Fighting had continued elsewhere while the Kherson ceasefire was in place, to allow civilians to evacuate the Russian-occupied city of Oleshky.