Ukrainian Prime Minister Volodymyr Hroysman says his country is suffering an "unprecedented" cyberattack but that "vital systems" are not being affected.

Although Ukraine initially seemed to be the target of the cyberattack on June 27 -- affecting government computer networks and websites of banks, major industrial enterprises, the postal service, Kyiv's international airport, and its subway system -- the attack also hit other countries and international companies around the world.

A Ukrainian government official said on June 27 that a version of the Wannacry ransomware had hit government networks and several public institutions in a widespread cyberattack.

Anton Herashchenko, an adviser to Interior Minister Arsen Avakov, said a version of Wannacry was being used.

"The ultimate goal of the cyberattack was to try to destabilize," he wrote on Facebook, adding that the attacks probably originated in Russia.

WannaCry is a virus that shut down more than 200,000 computers in some 150 countries in May, demanding that the computer users pay hundreds of dollars to regain use of their computer and not lose their data.

Ukrainian Deputy Prime Minister Pavlo Rozenko said on Facebook on June 27 that every computer monitor in the cabinet of ministers was locked and displayed a message in English warning users that if they shut down their computers all of their data will be deleted.

Rozenko said on Twitter that "the entire network is down in the government's secretariat. It has either been hacked or shut down by the security system. That's unclear."

The Ukrainian central bank said a number of Ukrainian banks were also affected by the attack -- which it described as being caused by an "unknown virus."

"As a result of these cyberattacks these banks are having difficulties with client services and carrying out banking operations," it said in a statement, without naming any of the banks affected.

"The central bank is confident that the banking infrastructure's defense against cyberfraud is properly set up and attempted cyberattacks on banks' IT systems will be neutralized," the statement added.

Attacks Hit Other Countries

Meanwhile, a growing list of international companies based in countries including the United States, the Netherlands, Germany, Britain, Denmark, Norway, France, Russia, and India also reported being affected by similar cyberattacks.

Russia's top oil producer, Rosneft, said its servers had been attacked, as had the Copenhagen-based international shipping company Maersk, French industrial group Saint-Gobain, the U.S.-based Merck pharmaceutical company, and the British advertising giant WPP.

Several other companies and organizations also reported having computer network problems.

A Swiss IT company, MELANI, said on June 27 that it appeared the virus Petya, a version of Wannacry, was being circulated again.

MELANI said in an e-mail that Petya had been blamed for affecting computer networks around the world in 2016.

Online security companies Bitdefender Labs and Kaspersky Labs said the virus was being spread because of a tool created by the U.S. National Security Agency known as EternalBlue, which allows malware to spread inside an organization's network.

In Ukraine, Prime Minister Hroysman said on Facebook that "the attack will be repelled and the perpetrators will be tracked down."

Oleksandr Turchynov, the secretary of Ukraine's Security and Defense Council, said there were signs of Russian involvement in the cyberattacks.

Ukrainian state power distributor Ukrenergo said its IT system had been hit by a cyberattack on June 27, but the disruption had "no effect on power supplies."

Several local power distributors also experienced disruptions due to the cyberattack, including Kyivenergo, Dniproenergo, and Zaporizhiaenergo, Interfax-Ukraine reported.

At the Chernobyl nuclear power station, which still produces energy for Ukraine, officials said some of the facility's routine radiation checks were being done manually because of the "disconnection" of some of its computer systems.

Anotonov, the Ukrainian state-run aircraft manufacturer, has also been hit by a cyberattack. A spokeswoman for the company said it was still unclear how serious the attack is.

Pavlo Ryabikin, the acting director of Kyiv's Boryspil airport, said on Facebook that a cyberattack on the airport's official website and digital flight schedule could cause flight delays.

Also in the capital, the Kyiv subway said on Twitter that its payment system had been hit by a cyberattack and credit-card payments were not being processed.

With reporting by Reuters, dpa, AP, Interfax, and Obozrevatel