Hackers have brought down several websites of the Ukrainian government amid a period of high military tension between the former Soviet state and Russia.

The Ukrainian government says the websites of the foreign and education ministries, plus other agencies, were down from Thursday evening into Friday.

The hackers posted a message written in Ukrainian, Russian and other languages saying, "Ukrainians! All data on the computer is destroyed and it is impossible to restore it. All information about you has become public. Be afraid and expect the worst."

The Ukrainian government is investigating who carried out the massive cyberattack. It says no leaks of personal information have been confirmed.

A foreign ministry spokesperson told the Reuters news agency that it was too early to say who could be responsible, while also pointing out that Russia was behind similar attacks in the past.

Fighting has continued between pro-Russia separatists and government forces in eastern Ukraine since Moscow annexed Crimea from the country in 2014.

Tensions remain high, and Russia has recently deployed about 100,000 troops near the border it shares with Ukraine.