Special police teams on Wednesday searched the airports in Sofia, Plovdiv, Varna and Burgas, as well as the offices of Bulgarian National TV and the leading newspaper "24 Hours" for explosive devices but none were found.
Police say "the apparent purpose was to disrupt their work."
They say the emails were sent using anonymizing Internet tools and online messaging providers based outside Bulgaria.
Bulgarian police are in contact with international law enforcement agencies as part of the investigation.
Police say similar messages were sent Tuesday to airports and later to media organizations in other EU countries but they did not identify them.
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