Hackers made a "very powerful" attack on the Kremlin website on September 13, the Russian government said on September 14.
Kremlin spokesman Dmitry Peskov linked the attack to regional elections in Russia over the weekend in which the opposition sought to challenge government-allied politicians in Kostroma Oblast, the one region it was allowed to run.
Peskov said the election commission's website came under attack in the morning.
"Given that, you will certainly be interested to know that from 5 to 10 a.m. on Sunday a very powerful attack was simultaneously carried out on the Russian president's website," Peskov said.
"Defense systems worked, though it was not easy. The attack was rather strong."
He said he had no information on who might have been behind the attack, which caused the website to shut down briefly.
Russia has a hacking criminal underground and the United States regularly accuses Russian hackers of attacks.
Experts say Russian government-backed hackers have targeted U.S. government computers and have helped spread Moscow propaganda at a time of poor relations between the Kremlin and the West over the conflict in Ukraine and other matters.