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. 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. 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. 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.”