A number of Ukrainian state institutions, banks and companies, including the state power distributor, and the country's main gateway to the world, were hit by a cyber attack on Tuesday that disrupted some operations, the Ukrainian central bank said.
The latest disruptions follow a spate of hacking attempts on state websites in late-2016 and repeated attacks on Ukraine's power grid that prompted security chiefs to call for improved cyber defenses.
According to Ukrainian Deputy Prime Minister's Facebook post, all computers in the government building were affected by the virus.
Director of Kiev's Boryspil Airport said IT-system was affected Tuesday by a cyber attack causing possible flight delays.
The central bank said an "unknown virus" was to blame for the latest attacks, but did not give further details or say which banks and firms had been affected.
"As a result of these cyber attacks these banks are having difficulties with client services and carrying out banking operations," the central bank said in a statement.
"The central bank is confident that the banking infrastructure's defense against cyber fraud is properly set up and attempted cyber attacks on banks' IT systems will be neutralised," it said.
Oschadbank, one of Ukraine's largest state-owned lenders, said some of its services had been affected by a "hacking attack" but guaranteed that customer data was safe.
Ukrainian state power distributor Ukrenergo said its IT system had been hit by a cyber attack, but the disruption had no impact on power supplies or its broader operations.
The widespread cyber attack also targeted several media outlets, including TRC "Lux" media holding, ATR TV channel, and popular news website "Korrespondent."
Ukrainian Prime MInister Volodymyr Groysman said that the cyber attacks were "unprecedented," but they failed to affect the most important systems.
Meanwhile, Russia's top oil producer Rosneft, metals giant Evraz, and several other companies were also targeted in the attack.
Rosneft and Evraz said their production had not been affected.
"The hacking attack could lead to serious consequences, but the company has moved to a reserve production processing system and neither oil output nor refining have been stopped," the oil company said on Twitter.
According to Russian media, the the culprit was a virus called "Petya.A," which operates similarly to the WannaCry virus that hit thousands of computers worldwide.
WannaCry ransomware, which started to sweep the globe May 12 and has infected more than 300,000 computers in 150 nations. It threatens to lock out victims who have not paid a sum of $300 to $600 within one week of infection.
Britain's WPP, the world's biggest advertising company, also said that computer systems within several of its agencies had been hit by a suspected cyber attack.
"IT systems in several WPP companies have been affected by a suspected cyber attack," the company said. "We are assessing the situation, taking appropriate measures and will update as soon as possible."
WPP owns agencies including JWT, Ogilvy & Mather, Young & Rubicam and Grey.
Swiss government agency said that Ukraine, Russia, England, and India were the most affected by the Petya.A virus, which demands users to pay $300 worth of Bitcoin in exchange for decryption key to recover personal files.
Ukraine has blamed Russia for previous cyber attacks, including one on its power grid at the end of 2015 that left part of western Ukraine temporarily without electricity.
Cyber security experts consider Russia one of the world's most advanced cyber powers, along with the United States, China, Israel, France and Britain.
Relations between Kiev and the Kremlin collapsed in 2014 following Moscow's annexation of Crimea and support for pro-Russian separatists in eastern Ukraine, where fighting continues despite a cease fire agreement.
Russia denies carrying out cyber attacks on Ukraine and allegations it has fueled the eastern conflict by suppling rebels with troops and weapons.