Paramedics prepare to enter a college after employees received a suspicious envelope, in the northern port city of Thessaloniki, Greece, Friday, Jan. 11, 2019. At least nine people have received medical attention after about a dozen letters containing a white powder described as consisting of "industrial irritants" were sent to 11 university and college offices around Greece, authorities said Thursday. (AP Photo/Giannis Papanikos)
camera (The Associated Press) Paramedics prepare to enter a college after employees received a suspicious envelope, in the northern port city of Thessaloniki, Greece, Friday, Jan. 11, 2019. At least nine people have received medical attention after about a dozen letters containing a white powder described as consisting of "industrial irritants" were sent to 11 university and college offices around Greece, authorities said Thursday. (AP Photo/Giannis Papanikos)

Greek authorities have searched at least 10 more university and college buildings after letters containing white powder were sent to campuses around the country.

Fire service crews for a third day Friday picked up more suspicious packages and carried out building inspections in Athens, the northern city of Thessaloniki, and several other towns, bringing the total number of incidents to 24. At least a dozen people have received medical attention as a precaution but none were hospitalized.

The Greek Civil Protection Authority said the letters had been mailed from India. Analysis of the first sample obtained by authorities showed the powder consisted of an industrial adhesive.

Police haven't commented on reports by state-run television that the letters contained printed "Islamic material" in English.