A group of Russian-speaking hackers has attacked recently a number of hospitals in the United States by using ransomware, the Wall Street Journal said on Thursday.

At least three hospitals were targeted in cyberattacks earlier this week, US-based cyber security firm Mandiant Chief Technology Officer Charles Carmakal said.

US analysts have linked the attack to an Easter European hacker group known as UNC1878, the report also said.

The FBI and the Department of Health and Human Services have issued a joint alert regarding the attack, providing detailed recommendations on how to defend against the threat.

UNC1878 currently does not appear to make efforts targeting the United States voting system just days ahead of the November 3 election, according to the report