Story highlights Amnesty International said its locks and alarm system had been removed

Notice on sealed front door warned people not to enter

(CNN) Authorities have sealed off Amnesty International's office in Moscow, the human rights group said Wednesday, adding it did not know why Russian officials would take such a step.

Staffers arrived at the office Wednesday morning to find it sealed with a notice from municipal authorities warning people not to enter, according to an Amnesty International statement

The locks and an alarm system had been removed, and the electricity supply appeared to have been cut off, the group said.

"We do not know what prompted Moscow authorities to prevent our staff from accessing our offices -- an unwelcome surprise for which we received no prior warning," said Amnesty International's Europe Director John Dalhuisen.

"Given the current climate for civil society work in Russia, there are clearly any number of plausible explanations, but it's too early to draw any conclusions," he said, adding he hoped there had been a "simple administrative explanation" for it.

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