"It could be a sign that the users represent a Russian-speaking country such as Russia, Ukraine or Belarus. But it is too early to draw any conclusions," IAAF doping chief Arne Ljungqvist told Sweden's largest broadsheet Dagens Nyheter.
Syringes, bottles, rubber tubes, phials and alleged banned substances were found in a plastic bag dumped in a rubbish bin on Monday near the Opal hotel, home to competitors from Russia, Poland, Bosnia, Montenegro, Malta and Gibraltar during the Championships which ended on Sunday.
Both the bag and the phials bore Russian text, according to the paper.
Police would not comment on the contents of the bag, and said on Monday analysis of the materials could take up to two weeks.
Meanwhile, cleaning staff at the Opal hotel reported finding empty syringes in Russian competitors' rooms, according to daily Aftonbladet on Tuesday.
Hotel staff were prevented from cleaning rooms occupied by the Russian team during the championships, and were permitted only to deliver new towels, according to an anonymous source quoted by the paper.
Russia ended the competition in Gothenburg with 12 golds but their achievement was questioned by Spain's athletics federation chief Jose Maria Odriozola on Monday.
"Russians have won more than 50 percent of the medals at the European championships ... and it's extremely suspicious," Odriozola said in an interview with Spanish newspaper El Mundo Deportivo.
Russian coach Valery Kulichenko described Odriozola's claim that his athletes cheated as provocative.
"It's not the first case of Odriozola trying to provoke us. Our doping control system was tested and approved by the IAAF and all of our athletes are under constant and complete control," Kulichenko said.