© Reuters. Man holds laptop computer as cyber code is projected on him in this illustration picture
One person familiar with the matter said the hack was so serious it had led to a National Security Council meeting at the White House on Saturday.
Kremlin spokesman Dmitry Peskov dismissed the allegations.
“Once again, I can reject these accusations and once again I want to remind you that it was President (Vladimir) Putin who proposed that the American side agree and conclude agreements (with Russia) on cyber security,” said Peskov, saying Washington had not responded to the offer.
“As for the rest, if there have been attacks for many months, and the Americans could not do anything about it, it is probably not worth immediately groundlessly blaming the Russians. We didn’t have anything to do with it.”
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