Russia has banned the export of medical specimens after the country's spy agency allegedly uncovered a Western plot to manufacture a biological weapon that would make Russians sterile.

In a decree that appeared to reflect the Russian state's growing suspicion of all things Western, the Federal Customs Service forbade the shipment of all human blood, hair, DNA and bone marrow out of the country.

While officials gave no formal explanation for the ban, Russia's most respected broadsheet suggested that the customs service had been ordered to act after the Federal Security Service, the KGB's successor, handed an alarming report to President Vladimir Putin earlier this month.

Quoting unidentified sources, Kommersant said that foreign health institutions were using human specimens to create a "genetically engineered biological weapon" capable of rendering the Russian population sterile or even of killing it off altogether.

Among those purportedly involved in the conspiracy are the Harvard School of Public Health and the U.S. Department of Justice. The FSB declined to comment on the allegations.

The newspaper said the ban had been authorized by deputy prime minister Sergei Ivanov, a hardliner many believe could succeed Mr Putin next year.

Doctors have expressed concern that the ban could lead to thousands of unnecessary deaths. Hundreds of biological samples are shipped out of Russia every day for clinical trials that cannot be carried out locally.

It is unclear whether individual samples, which are often sent for analysis abroad allowing life-saving diagnosis for many curable diseases, are affected.

Officials at the Federal Customs Service said they had been "expressly forbidden" from releasing details about the ban. A health ministry spokesman said it was possible individual samples were exempt.

"We have nothing to do with the ban," the spokesman said. "As far as I know, it primarily targets clinical trials conducted by pharmaceutical companies." Like many foreign companies operating in Russia, pharmaceutical multinationals have come under growing official suspicion of late, with some accused of improperly carrying out tests on children.