Moscow: A new wave of powerful cyberattacks hit Europe on Tuesday in a possible reprise of a widespread ransomware assault in May that affected 150 countries, as Ukraine reported ransom demands targeting the government and key infrastructure, and the Danish Maersk conglomerate said many of its systems were down.

The Russian oil giant Rosneft was also hit, as was the British advertising and marketing multinational WPP. Norway's National Security Authority said an "international company" there was affected.

Ukraine first reported Tuesday's cyberattacks, saying they targeted government ministries, banks, utilities and other important infrastructure and companies nationwide, airport departure tables and demanding ransoms from government employees in the cryptocurrency bitcoin.

By midafternoon, breaches had been reported at computers governing the municipal energy company and airport in Ukraine's capital, Kiev, the state telecommunications company Ukrtelecom, the Ukrainian postal service and the State Savings Bank of Ukraine.

Ukrainian Deputy Prime Minister Pavlo Rozenko on Tuesday tweeted a picture of a computer screen warning in English that "one of your disks contains errors," then adding in all capital letters: "DO NOT TURN OFF YOUR PC! IF YOU ABORT THIS PROCESS, YOU COULD DESTROY ALL YOUR DATA!"

"Ta-Dam!" he wrote. "It seems the computers at the Cabinet of Ministers of Ukraine have been 'knocked out.' The network is down." Other shots of computer screens attributed to government officials showed demands for a "ransom" of $300 in bitcoins to release data encrypted by the virus.

Ukraine's National Bank said in a statement that an "unknown virus" has caused banks "difficulties in serving clients and carrying out banking operations."

Some radiation checks at the Chernobyl nuclear disaster site in Ukraine were being carried out manually on Tuesday after the attacks affected operations, a state agency said.

"Due to the temporary disconnection of Windows systems, radiation monitoring of the industrial site is being carried out manually," the state agency that oversees the Chernobyl exclusion zone said in a statement.

A representative of the agency told Reuters only the radiation checks on personnel entering and leaving the zone were being done manually, while all other radiation monitoring was being carried out as normal.

"All technology systems of the station are working as normal," the agency said.

The hack's scale and the use of ransomware quickly recalled the massive May cyberattack in which hackers likely linked to North Korea disabled computers in dozens of nations, including Ukraine, using a flaw that was once incorporated by the National Security Agency's surveillance tool kit.

Whatever its source, the virus appeared to be spreading on Tuesday. Maersk, a Danish transport and energy conglomerate, announced that "Maersk IT systems are down across multiple sites and business units due to a cyber attack."

Separately, the Russian oil giant Rosneft announced that its servers has been hit by a "powerful hacking attack," which knocked the company's website offline on Tuesday afternoon.

Apparently referring to a conflict over a regional oil producer with the Russian conglomerate Sistema, owned by oligarch Yevgeny Yevtushenkov, Rosneft's statement added: "We hope that this has nothing to do with the current court proceedings." There was no information immediately available tying the alleged attack to the Ukrainian hack.

Washington Post, Reuters