A number of government websites in Ukraine were down on Friday after a huge hacking attack, officials and media reports said.

While it is not immediately clear who was behind the attacks, they come amid heightened tensions with Russia as talks between Moscow and the west this week failed to yield any significant progress.

Ukraine's foreign ministry spokesman Oleg Nikolenko wrote on Facebook: "As a result of a massive hacking attack, the websites of the ministry of foreign affairs and a number of other government agencies are temporarily down. Our specialists are already working on restoring the work of IT systems."

According to the Ukrainskaya Pravda newspaper, websites of the country's cabinet, seven ministries, the treasury, the national emergency service and the state services website - where Ukrainians' electronic passports and vaccination certificates are stored - were unavailable as the result of the hack.

The report also said that the foreign ministry's website contained a message in Ukrainian, Russian and Polish, saying that Ukrainians' personal data has been leaked to the public domain.

"Be afraid and expect the worst. This is for your past, present and future," the message read.

Ukraine's security officials have said that no personal data has been leaked.

The US estimates Russia has massed about 100,000 troops near Ukraine, a build-up that has stoked fears of an invasion.

Moscow says it has no plans to attack and rejects Washington's demand to pull back its forces, saying it has the right to deploy them wherever necessary.

The Kremlin has demanded security guarantees from the west precluding Nato's expansion eastwards.

Last month, Moscow submitted draft security documents demanding that Nato deny membership to Ukraine and other former Soviet countries and roll back the alliance's military deployments in Central and Eastern Europe.

Washington and its allies have refused to provide such pledges, but said they are ready for the talks.

High-stakes talks this week between Moscow and the US, followed by a meeting of Russia and Nato representatives and a meeting at the Organisation for Security and Cooperation in Europe failed to yield any progress.