Ukraine’s national postal service Ukrposhta was the victim of a cyberattack on Friday.

The attack, which is still unclear, came after sales of a postage stamp depicting a Ukrainian soldier making a crude gesture to a Russian warship went online.

The Director General of Ukrposhta, Ihor Smilianskyi, confirmed the incident and stated that the attack was a DDoS (distributed denial-of-service) attack.

“We are really doing everything, together with internet providers, to restore both the online store and other Ukrposhta systems that are also temporarily not working due to a DDoS attack on our systems,” Smilianskyi wrote on Facebook.

The stamp went online after the flagship of Russia’s Black Sea fleet sank. While Ukrainian officials claimed that Ukraine hit the cruiser Moskva with missiles, Russia said the ship sank in stormy seas after a fire was triggered by an explosion of ammunition.

Ukraine continues to suffer from several cyberattacks before and after Russia’s incursion into the country on 24 February. The attackers behind the attack on Ukraine’s national postal service have not yet been identified.