The US Department of Defense must present proof that its biomaterials research does not violate international law, Russian Foreign Ministry spokeswoman Maria Zakharova told a news briefing on Thursday.

"The official explanations the Pentagon has offered do not sound convincing in this particular case," she said.

"We believe that the US Ministry of Defense must present convincing proof that the US Air Force’s biomaterials research under this contract does not violate international law."

Moscow is concerned over reports about Pentagon’s studies of genetic material collected from Russian citizens on Russia’s territory, Zakharova stressed.

"We are highly concerned over the fact that the US Department of Defense is conducting studies of genetic material collected from Russian citizens on Russia’s territory," she said.