(Photo: AP)

THE HAGUE, Jan. 3 (Xinhua) -- Following several bomb letters in recent days, a new bomb letter was reported on Friday at the Okura Hotel in the south of Amsterdam, according to the Dutch police.

Employees from the mail room of the hotel found the letter and sounded the alarm. The hotel did not have to be evacuated, said the police.

The Dutch Explosives Clearance Defense Service is now investigating the incident.

Similar bomb letters have been posted to different companies at different locations of Dutch cities, with two in Amsterdam, one in Utrecht and three in Rotterdam over a period of one week.

"The bomb letters did not cause any damage, because the explosives did not go off, but could have caused serious physical injury," the police stated.

The police take into account that there is one and the same sender of the letters. The motive is still unclear.

The letters had a sticker of the CIB, the Dutch Central Collection Office, based in Rotterdam. One of the letters was found at the CIB headquarters on Jan. 2. The criminal investigation has shown that the company has no involvement in this case.