Ukraine on Monday accused unnamed Russian internet networks of massive attacks on Ukrainian security and defense websites, but gave no details of any damage done or say who it believed was behind the assault.
Kyiv has previously accused Moscow of orchestrating large cyber attacks as part of a "hybrid war" against Ukraine, which Russia denies.
However, a statement from Ukraine's National Security and Defence Council did not disclose who it believed organized the attacks or give any details about the effect the intrusions may have had on Ukrainian cyber security.
The attacks started on Feb. 18 and were directed against websites belonging to Ukraine's Security Service, the council itself and some other state institutions and strategic enterprises, it said in a statement.
"It was revealed that addresses belonging to certain Russian traffic networks were the source of these coordinated attacks," the Council said.
The council added the attacks attempted to infect vulnerable government web servers with a virus that covertly made them part of a botnet used for so-called distributed-denial-of-service (DDoS) attacks on other resources.
A DDOS attack is a cyber attack in which hackers attempt to flood a network with unusually high volumes of data traffic in order to paralyze it.
Ukraine and Russia have been at loggerheads since Russia's annexation of Crimea from Ukraine in 2014 and involvement in a conflict in Ukraine's eastern Donbass region which Kyiv says has killed 14,000 people.
Ukraine's army said this month that five of its service personnel were killed over the week ended on Feb. 14 despite a ceasefire with pro-Russian separatists in the east of the country.
On Monday, the military reported another dead soldier who came under fire from an anti-tank grenade launcher.