Social media platform X went down intermittently on Monday, with owner Elon Musk blaming an unusually powerful cyberattack.

“We get attacked every day, but this was done with a lot of resources. Either a large, coordinated group and/or a country is involved,” Musk said in a post on X earlier Monday.

He did not clarify exactly what he meant by “a lot of resources” and his comments drew skepticism from cybersecurity specialists, who pointed out that attacks of this nature — called denials of service — have repeatedly been executed by small groups or individuals.

X faced intermittent outages, according to Downdetector, restricting 39,021 users in the US from accessing the platform at its peak at 10am ET. By 5 p.m., there were reports of the service being down for roughly 1,500 users.

A source in the internet infrastructure industry said X had been hit by several waves of denial of service beginning around 9:45 UTC. The source spoke on the condition of anonymity as the person was not authorized to speak publicly on the matter.

Denial of service works by overwhelming targeted websites with rogue traffic. Such attacks are not necessarily sophisticated but they can cause significant disruption.

Musk later said in an interview with Fox Business Network’s Larry Kudlow the cyberattack came from IP addresses originating in the Ukraine area.

The industry source disputed Musk’s account, saying that large chunks of the rogue traffic bombarding X could be traced back to IP addresses in the United States, Vietnam, Brazil and other countries, and that the amount of rogue traffic coming directly from Ukraine was “insignificant.”

In any case, denial of service attacks are notoriously hard to trace back to their authors and the IP addresses involved rarely provide any meaningful insight into who was behind them.

Musk has joined US President Donald Trump, whom he serves as an adviser, in criticizing Ukraine’s continued efforts to fight off a Russian invasion. Musk said on Sunday that Ukraine’s front line “would collapse” without his Starlink satellite communications service, though he said he would not cut off Ukraine’s access to it.