Hackers have caused widespread disruption across Europe, hitting Ukraine especially hard.

A number of Ukrainian banks and companies, including the state power distributor, have been hit by a cyber attack that disrupted some operations.

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 defences.

Company and government officials reported major disruption to the Ukrainian power grid, banks and government offices. Russia's Rosneft energy company also reported falling victim to hacking, as did shipping company A.P. Moller-Maersk, which said every branch of its business was affected.

"We can confirm the breakdown is caused by a cyber attack," a spokeswoman said.

Ukraine's Deputy Prime Minister Pavlo Rozenko on Tuesday posted a picture of a darkened computer screen to Twitter, saying that the computer system at the government's headquarters has been shut down.

There is little information about who might be behind the disruption, but technology experts who examined screenshots circulating on social media said it bears the hallmarks of ransomware, the name given to programs that hold data hostage by scrambling it until a payment is made.

Kiev's main airport was also hit with an attack which may cause flight delays, operator Boryspil said on Facebook.

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.