Amazon Madrid office bomb threat 'false'; staff back to work

Amazon's office in the Spanish capital Madrid has been evacuated following a telephone bomb threat, Spanish police said on Thursday.

"An alert has been received and we're investigating," a police spokeswoman said.

Update: "It was a false alarm,", a police spokeswoman said, adding that Amazon's staff were re-entering the building. An Amazon spokesman confirmed staff were back to work.

The incident comes as Netherlands police investigate letter bombs sent to different cities including the capital Amsterdam.

A letter bomb exploded at a bank headquarters in Amsterdam on Thursday, a day after two other businesses were targeted in what Dutch police said was an extortion attempt.

The suspected blackmailer in the earlier attacks had demanded payment in bitcoins -- a virtual currency -- and threatened further blasts if the companies failed to make payment.