(BBC) A mysterious Russian satellite displaying "very abnormal behaviour" has raised alarm in the US, according to a State Department official.

"We don't know for certain what it is and there is no way to verify it," said assistant secretary Yleem Poblete at a conference in Switzerland on 14 August.

She voiced fears that it was impossible to say if the object may be a weapon.

Russia has dismissed the comments as "unfounded, slanderous accusations based on suspicious".

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