Pages which usually show statements from the UN Secretary General Ban Ki-Moon were replaced with messages accusing the US and Israel of killing children.
That section of the site was taken down, but the breach was rectified with in a few hours.
A UN spokesman confirmed the breach, saying: "We are very concerned that this happened and we are investigating. We will make security changes to prevent this from happening again."
Before the message the hacked UN page also contained the text: “Hacked By Keremy 125 M0sted And Gsy. That Is CyberProtest”
CyberProtest appears to be a group based in Turkey, with media reports claiming their agenda is to spread the message "that the powerful have no right to oppress the powerless."