Ukraine’s worst cyberattack in four years brought down the websites of scores of government agencies for hours. Authorities didn’t immediately identify the source of the hacks, which took place as tensions with Russia intensified over its troop buildup across the border.

Seventy government agencies were hit, including the Foreign and Agriculture Ministries, Viktor Zhora, the deputy head of the state agency in charge of special communication and information protection, said Friday. Authorities are investigating and would have their first conclusions later in the day, he said.

“There was no leak of important data, the content of the websites was not damaged,” Zhora said. “We are collecting digital evidence and analyzing data to understand the full chain of this attack.”

Ukraine has previously accused Russia of mounting major cyberattacks against its digital infrastructure. Relations between the two former Soviet partners have worsened since the ouster of a Russian-backed president in 2014 and Moscow’s subsequent annexation of Crimea.

In recent months, Ukraine and its allies in the U.S. and Europe have warned that Russia could be preparing to invade as it massed about 100,000 troops near the border. Moscow denies any such plans.

No group claimed responsibility for the cyberattack, and a Kremlin spokesman didn’t respond to a request for comment. EU foreign policy chief Josep Borrell said the bloc would help Ukraine, while NATO Secretary General Jens Stoltenberg condemned the attack and said the military alliance would continue its support for Kyiv.

During the attack, the Ukrainian Foreign Ministry’s site showed messages in the Russian, Polish and Ukrainian languages riddled with grammatical errors.

“Ukrainian! All your personal data has been uploaded to the public network,” the message said. “All data on your computer is being erased and won’t be recoverable. All information about you has become public, fear and expect the worst. This is being done to you for the your past, present and future,” it said, with a reference to “historic lands.”

— Bloomberg News