WASHINGTON (AP) — U.S. officials have not determined who was behind an apparent cyberattack on the social media site X that limited access to the platform for thousands of users, according to a Trump administration official familiar with the ongoing investigation into the matter.

Monday’s outage was described as a cyberattack by the official, who was not authorized to comment publicly on the matter and spoke Tuesday on the condition of anonymity. The official added that the Republican administration takes all cyberattacks against American companies seriously but underscored that the U.S. government had not gleaned any specific intelligence about who might have been behind the attack.

The comments came after Elon Musk, the billionaire owner of X and a top adviser to President Donald Trump, claimed in an appearance on Fox Business Network’s “Kudlow” show that the cyberattackers had “IP addresses originating in the Ukraine area” without going into detail on what that might mean.

Cybersecurity experts quickly pointed out, however, that this doesn’t necessarily mean that the attack originated in Ukraine.