Websites of Ukraine's president and security service attacked

It did not say who was behind the attack.

Kyiv has previously accused Russia of orchestrating cyber attacks as part of a "hybrid war" against Ukraine. Russia denies this.

Kyiv and Moscow have been at loggerheads since Russia annexed the Crimea peninsula from Ukraine in 2014 and backed separatists in a conflict in Ukraine’s eastern Donbass region which Kyiv says has killed 14,000 people.