Ukraine is coming under a "massive" cyberattack, a senior minister said on Wednesday, with the main websites of the government and foreign ministry refusing to open.

Deputy Prime Minister Mykailo Fyodorov said the attack began in the late afternoon and affected several banks as well as official websites, without specifying its origin.

The official site of Ukraine's cabinet of ministers and the foreign ministry refused to open when AFP tried to access it on Wednesday.

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But most of the main news sites in Ukraine were working, as well those of banks and the main public institutions.

Fyodorov said the functioning sites had managed to "switch traffic to a different provider to minimize the damage."

The sites of several ministries and banks also went down for a few hours last week, with officials suggesting the denial-of-service (DDoS) attack was of Russian origin.

Ukraine is facing mounting fears of a Russian invasion, which have intensified after the Kremlin recognized the independence of Ukraine's two eastern separatist region.

Russian President Vladimir Putin has also approved the deployment of troops into east Ukraine, although he said Tuesday that he has not yet decided to order the move.

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