Russia's foreign ministry on Sunday said an old version of its website had been attacked after a US hacker claimed he broke in and posted a mocking message.

Foreign ministry spokeswoman Maria Zakharova wrote on Facebook that the hacker targeted "an old site that has not been used for a long time," adding that "specialists are working out what happened."

The attack came after Washington earlier this week formally accused the Russian government of trying to "interfere" in the 2016 White House race by hacking, charges the Kremlin has repeatedly dismissed.

"If they establish there was hacking by Americans, even of a resource that wasn't working, this is far from pleasant," Zakharova wrote.

She said that this could be an indication that a "cyber machine of destruction has started acting" after US Vice President Joe Biden told NBC television that President Vladimir Putin would get a "message" from Washington in response to the hacking blamed on Russia.

Alternatively, the latest hack simply shows that the "US elections have wound up people to such a state that they start smashing everything," Zakharova wrote.

The foreign ministry's main website was apparently working normally on Sunday afternoon.

On Saturday, a hacker who calls himself the Jester tweeted: "I'm Jester & I approve this message via the Russian Foreign Affairs Website."

The hacker, who has previously attacked WikiLeaks website, posted a link to a page which which had content replaced with a message and an image of a jester.

"Comrades! We interrupt regular scheduled Russian Foreign Affairs Website programming to bring you the following important message," he wrote.

- 'This is America' -

"Knock it off. You may be able to push around nations around you, but this is America. Nobody is impressed," he added.

CNN reported that the jester's attack overnight Moscow time included the piercing sound used for civil alert messages about extreme weather.

The hacker said he was writing on the ministry site to complain after waves of distributed denial of service (DDoS) attacks pounded Twitter, Netflix and other major websites on Friday, accusing Russia of being behind this.

"Now, you can do the usual, shrug, smirk and say 'there's no evidence' that points to Russia being behind any of this stuff, and you can get the Russian Ambassador to US to post some mildly amusing quips over Twitter."

"But let's get real, I know it's you, even if by-proxy, and you know it's you," the hacker wrote.

On Sunday, after the Zakharova's Facebook message, Jester tweeted, "#OutPropagandered - Getting Russia to admit they got 'dinged'. Priceless. They've already started tweaking the story," with a link to a somewhat dismissive article on the pro-Putin Russia Today website.

The mass DDoS attack on Friday could have been meant as a message from a foreign power, cyber security analysts told AFP at the time.

The onslaught commanded the attention of top US security agencies, including the Department of Homeland Security.

"DHS and the FBI are aware and are investigating all potential causes" of the outages, a spokeswoman said.

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