Ukraine said a cyberattack brought down the websites of several government agencies Friday. Authorities didn’t immediately comment on the source of the outage, which comes amid surging tensions with Russia due to its buildup of thousands of troops near the border.

A spokesman for Ukraine’s Foreign Ministry said on Twitter that the websites were down following a massive hack and that authorities were working to restore services. He didn’t identify who might be behind the attack, which hit the site of his agency as well as those of the Agriculture and Education Ministries and the government staff.

All those sites were down, some with their content replaced for a time by messages in Russian, Polish and Ukrainian.