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A cyberattack hit the websites of Ukraine’s defense ministry and armed forces, and the websites of two Ukrainian banks on Feb. 15, Ukrainian government agencies announced. The incident comes over the backdrop of persisting tensions over the threat of a possible Russian invasion.

The State Service of Special Communications and Information Protection of Ukraine (SSSCIP) told cnn.com it was not clear who was behind the attack.

At least 10 Ukrainian websites were unreachable due to the attacks, including the defense, foreign and culture ministries and Ukraine’s two largest state banks. Customers at Ukraine’s largest state-owned bank, Privatbank, and the state-owned Sberbank reported problems with online payments and the banks’ apps.

SSSCIP identified the incident as a distributed denial of service (DDoS) attack, which floods a website with phony traffic to disrupt access to it. DDoS attacks are relatively cheap and easy to carry out. While they can be disruptive, they do not necessarily require sophistication.

Ukrainian government officials “continue to monitor and cut off” the Internet Protocol (IP) addresses from which the hackers are flooding Ukrainian websites with traffic, according to SSSCIP.

A separate cyberattack hit Ukrainian government websites last month. Ukrainian officials suggested Russian and Belarusian involvement, but investigators have not formally blamed those countries for the cyberattack, according to international news agencies.