The attack on websites, including those of the cabinet and several ministries, came as tensions with the West and Russia continue to escalate.
Kiev has reported a massive cyberattack on key government websites as tensions between Russia and the West over Ukraine escalate following several rounds of unsuccessful talks.
The education ministry said on Facebook that its website was down due to a "global (cyber) attack" that had taken place overnight on Friday.
Other websites that were down, including that of the cabinet and the foreign and emergencies ministries. No one immediately claimed responsibility for the attack.
The foreign ministry website temporarily displayed a message in Ukrainian, Russian and Polish that appeared to suggest the attack was in response to Ukraine's pro-Western stance.
"Ukrainians! All of your personal data .. have been deleted and are impossible to restore. All information about you has become public, be afraid and expect the worst."
"This is for your past, present and future. For Volyn, OUN, UPA, Galitsia, Polesye and for historical lands," it said, referring to ultra-nationalist organisations and regions of Ukraine.
However, the Ukrainian government said on Friday that the content of the websites was not changed during the attack and no personal data was leaked.
Not hard to 'imagine who is behind'
The European Union is mobilising "all its resources" to aid Ukraine after the attack, EU foreign policy chief Josep Borrell said on Friday.
Borrell said that ambassadors of the EU's political and security committee would convene for an urgent meeting on the attack, which he added "merits condemnation". "There is no evidence who is behind the attack, but we can imagine who is behind," he said.
The education ministry said that authorities, including the SBU security service and cyberpolice, were working to address the issue.
The attack comes as tensions between Russia and the West soar over Ukraine, a strategic ex-Soviet country.
The West has accused Russia of deploying tanks, artillery and about 100,000 soldiers on Ukraine's war-torn eastern border in recent weeks. According to NATO, Russia is preparing for an invasion. Moscow says it has no plans to invade Ukraine.
This week the United States and its NATO allies held talks with Russia in an attempt to ease tensions, but all three rounds of negotiations - in Geneva, Brussels and Vienna - proved unsuccessful.
On Thursday, Deputy Foreign Minister Sergei Ryabkov said Moscow saw no reason to hold a new round of security talks with the West following a lack of progress.