The head of Ukraine's cyberpolice has claimed that Russian hackers are infecting computer systems of Ukrainian firms with malware to establish "back doors" for a large-scale coordinated attack.

Serhiy Demedyuk told Reuters news agency that banks and energy infrastructure firms are among the targets of the alleged hackers, and added that Ukrainian police are working with foreign authorities to identify the culprits.

Kremlin spokesman Dmitry Peskov denied the allegations. "No, that is not true," Peskov said in comments sent to Reuters by his office.

Law enforcement and private security firms throughout the world are carefully monitoring threats in Ukraine, because the country was at the origin of some of the most serious cyberattacks in history.

Some attacks have occurred on major Ukrainian holidays, and Demedyuk said another one could be launched on June 28 -- Constitution Day -- or on Independence Day in August.

"Analysis of the malicious software that has already been identified and the targeting of attacks on Ukraine suggest that this is all being done for a specific day," Demedyuk said.

In June 2017, a virus dubbed NotPetya hit the country and disabled government departments and state companies before spreading to corporate networks around the globe, inflicting losses of billions of dollars.

The United States and Britain joined Ukraine in blaming Russia for the NotPetya attack.

Relations between Kyiv and Moscow are at an all-time low after Russia seized the Crimea region in 2014 and fomented separatism in eastern Ukraine, where more than 10,300 people have been killed in the ensuing war.

Kyiv has accused Russia of being behind large-scale cyberattacks as part of a "hybrid war" against Ukraine. Moscow denies the accusations.

Based on reporting by Reuters