In Moscow, pig DNA has been identified in sausages produced at a halal meat processing plant.
However, this does not necessarily mean that the products actually contain pork, a spokesman for the institute that conducted the tests said.
"The DNA traces that have been discovered may be a result of contact with raw meat consisting of pork or pork products," said Boris Gutnik of the Gorbatov All-Russian Meat Research Institute.
He said the discovery did not necessarily mean that the products should be prohibited under the halal law, saying that the analysis that was used to conduct the tests could be "inexact".
Gutnik called for checks to be conducted at slaughterhouses, saying that if cattle were slaughtered in the same place as pigs, that could explain the presence of the pig DNA in the halal products.
The spokesman said that all the facilities and equipment that Moscow's Tsaritsino meat processing plant uses to produce halal meat are "completely separate from other processes".
Additional tests for the presence of pig DNA in the meat products will be conducted at three independent testing centers in Russia and one centre abroad.
The Tsaritsino meat processing plant has been supplying halal meat products to the Russia Mufties Council's International Center for Halal Standardization and Certification since 2007.