Over the weekend, threat actors defaced the website of the US Federal Depository Library Program (FDLP), in what could be the first Iranian state-sponsored cyberattack in retaliation for the US drone strike that killed Iranian military commander Maj. Gen. Qassim Suleimani at Baghdad airport last Friday.

In the wake of that attack, Iran had warned it would retaliate against the US in cyberspace, prompting the US Department of Home Security (DHS) to issue a rare National Terrorism Advisory System (NTAS) alert on Saturday.

The FDLP website was taken down after the defacement, which according to the DHS involved “pro-Iranian, anti-US messaging.” However, the DHS stressed that “at this time, there is no confirmation this was the action of Iranian state-sponsored actors.”

Read more: First Suleimani Attack By ‘Iranian’ Hackers Hits U.S., Exposing ‘Noisy’ New Threat