Two of Ukraine's banks have been targeted in a cyber attack, according to the country's security experts.
The country's largest state-owned banks PrivatBank and Oschadbank have been affected by the strike, with the country's Ministry of Defence website also reportedly crashing.
It comes amid fears that a Russian cyber attack may precede a possible invasion of Ukraine.
Websites for Oschadbank and Ukraine's Ministry of Defence were down when The Mirror tried to access them this afternoon.
The Centre for Strategic Communications and Information Security of Ukraine, known as the Stratcom Centre, confirmed that the PrivatBank app had gone down for some users.
The Stratcom Centre, which is part of the Ukrainian Government and counters online threats, wrote on Facebook: "During the last hours 'PrivatBank' is under a massive DdoS-attack.
"Privat24 users report problems with payments and in general with the operation of the app. Some users are completely unable to access Privat24, others do not reflect balance and recent transactions.
"There is no threat to investors' funds. Cyberattack is exclusively related to the Privat24 app. The rest of the financial transactions are carried out in a normal manner.
"In the work of 'Oschadbank' there are also errors, internet banking does not work.
"Also suffered attacks on the sites of the Ministry of Defence and the Armed Forces. It is no exception that the aggressor has succeeded in the tactics of small hoods, because most of his aggressive plans are not working."
The Stratcom Centre's LinkedIn page says it was established under Ministry of Culture and Information Policy of Ukraine and focuses on tackling disinformation and external threats, particularly from Russia.
PrivatBank told Ukrainian broadcaster Hromadske that it was able to withstand the cyber attack, which lasted for several hours.
It added that ATMs and self-service terminals did not work for around an hour.
The Mirror's defence editor Chris Hughes previously predicted Russia could launch a cyber attack on Ukraine.
Tensions between the two countries have reached fever pitch as the prospect of a full-blown invasion looms.
Russian soldiers test fired the OTR-21 Tochka-U missile system near Ukraine's border today as part of joint military drills with Belarus.
Meanwhile, more than 130,000 Russian troops are massed on the border of Ukraine, with US spies warning of a scheduled assault on Wednesday.
A senior American source told the Mirror that the Kremlin will order an attack at 3am local time on Wednesday.
Announcing it had been hit by a cyber attack, Oschadbank wrote on its Facebook page: "Oshchadbank informs that it suffered DDoS attacks.
"At the same time, we note that all banking systems are protected and operating as usual.
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"Currently, there is only a slowdown of access to the Oshhad24/7 system due to additional load on the communication channels.
"We apologise for the possible temporary inconvenience. We're working together to restore the system's regular speed."
Ukraine's Ministry of Defence also confirmed a DdoS attack.
It wrote on its Facebook page: "The official web portal of the Ministry of Defense of Ukraine suffered, probably, DDoS-attack when the excessive number of calls per second was fixed.
"Scheduled technical work is currently underway on the restoration of the regular functioning of the web portal of the Ministry of Defense of Ukraine."