Lithuanian state and private institutions were hit by a denial-of-service cyberattack on Monday, the Baltic country's National Cyber Security Centre said in a statement released by the defence ministry.
"It is very likely that attacks of similar or greater intensity will continue in the coming days, especially in the transportation, energy and financial sectors," the centre said.
Lithuania's tax authority said in a statement it had halted all activities due to an unusually large number of attempts to connect to its systems, although all data was safe.
"The main targets are state institutions, transport institutions, media websites," deputy Defence Minister Margiris Abukevicius said, in another sign of deteriorating relations between Baltic NATO country Lithuania and neighbouring Russia because of Moscow's invasion of Ukraine in February.
Soon after, Russian hacker group Killnet claimed responsibility for the distributed denial of service (DDoS) cyberattack on Lithuania, saying it was in response to Vilnius's decision to block the transit of goods sanctioned by the European Union to the Russian exclave of Kaliningrad.
"The attack will continue until Lithuania lifts the blockade," a spokesperson for the Killnet group told Reuters. "We have demolished 1652 web resources. And that's just so far."
Kaliningrad is connected to the rest of Russia by a rail link through Lithuania, a member of the EU and NATO.
Kaliningrad is sandwiched between EU and NATO members Poland and Lithuania and supplied by rail via Lithuanian territory.
Lithuania had begun to see signs of an attack as early as June 21, Abukevicius said.
A Russian Security Council spokesperson on June 22 promised retaliation over the blocked shipments, stating that these would have "a serious negative impact on the population of Lithuania".
European Union foreign policy chief Josep Borrell said last week Lithuania "only applies the European Union sanctions" in ceasing transport of certain goods to Kaliningrad, and has not taken any unilateral decisions.
© Thomson Reuters 2022