The cyberwar began Saturday and is still continuing, the radio network said in a statement Monday. It said the attackers have been using a denial-of-service attack that floods the computer servers with fake traffic so that legitimate visitors cannot get through.
The attack is aimed mainly on the web site of the radio's Belarus service, but web sites in Iran, Russia, Azerbaijan, Tajikistan, Kosovo, Macedonia, Bosnia and Croatia have also been affected, it said.
The broadcaster said it was taking measures to restore service at the web sites.
Jeffrey Gedmin, the network's president, compared the attack to the situation during the Cold War when broadcasting to communist countries was jammed.
"Dictators are still trying to prevent the kind of unfiltered news and information that RFE/RL provides from reaching their people," Gedmin said. "They did not succeed in the last century, and they will not succeed now."
The head of the radio's Belarussian service, Alexander Lukashuk, said the attack began on the 22nd anniversary of the Chernobyl nuclear catastrophe in neighboring Ukraine. He said a similar attack took place the same day one year ago, but lasted only for hours and did not hit services in other languages.
"We have a large Internet audience [in Belarus] that was relying on us to report live on a rally of thousands of people protesting the plight of uncompensated Chernobyl victims and a government decision to build a new nuclear power station," he said.
The broadcaster suggested that the government of authoritarian Belarussian President Alexander Lukashenko could be behind the attack.
"It's very hard to be certain in these cases, but because the target was the Belarus service, it does look like it's coming from the Belarus government," said Diane Zeleny, spokeswoman for the broadcaster.
"For our listeners in Belarus, it's quite dramatic," Zeleny said. "They cannot reach us right now. This is a pretty massive attack."
The press service of the Belarussian Information Ministry declined to comment.
"The government regularly blocks the largest information sites" when big protests are held, said Alexander Milinkevich, the most prominent figure in Belarus' beleaguered opposition.
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