Russian authorities have detained teenagers suspected of making some of the anonymous phone calls that have led to the evacuations of more than 150,000 people in two dozen cities across Russia, the Kommersant business daily reported Friday.

The bomb scares that swept nearly 500 malls, schools and transport hubs in cities including Moscow and St. Petersburg since Sunday have been downplayed by state-run television channels and the Federal Security Service (FSB) has instructed local authorities not to comment on the hoaxes to avoid copycat calls, the Vedomosti newspaper reported Friday.

However, the deputy governor of St. Petersburg said on Friday that the encrypted calls originated from abroad. “I cannot say yet what specific areas these calls came from, but I have no doubt that we will find out,” Alexander Govorunov was cited as saying by the Fontanka news outle/p>

The governor of the Kemerovo region — where more than a dozen schools, hospitals, and government buildings were cleared on Wednesday — said the wave of anonymous calls was just the beginning. “I believe that we should get used to this,” Aman Tuleev was cited as saying by local media on Friday. “The further we go, the worse it will get.”

One of the suspects is a 17-year-old who was detained in the Moscow region town of Volokolamsk on charges of falsely reporting an act of terrorism, Kommersant reported on Thursday.