May 29, 2017 0312 GMT
"No details have been provided which once again proves that these accusations are groundless," he said.
According to the Russian presidential spokesman, "taking into account the decisions that Ukraine made yesterday, this is just another example of Kiev’s Russophobic policy."
On Tuesday, Poroshenko signed an expanded blacklist consisting of 1,228 Russian individuals and 468 companies. This time, a number of the Russian State Duma members, judges from the Russian Constitutional Court, journalists and TV channels have been added to the blacklist.
Besides, sanctions have been slapped on several Russian companies, including 1C, ABBYY and their Ukrainian subsidiaries. In addition, Russia’s VKontakte and Odnoklassniki social networks, Mail.ru and Yandex internet companies have been banned as well.
The sanctions will remain in effect for three years.
The Ukrainian presidency said its website had been attacked by Russia in apparent retaliation for Kiev's decision to block prominent Moscow-based social networks.
"We have been witnessing the Russian response to the president's decree about closing access to Russian social networks," President Petro Poroshenko's deputy administration chief Dmytro Shymkiv said in a statement posted late Tuesday on Facebook.
IT specialists and Western governments are rarely able to pin a hacking attack directly on the Kremlin but often accuse groups or individuals close to the Russian government of being responsible for them.