The Pentagon on Tuesday added Britain to the list of countries that received live anthrax samples from the U.S. military.

Army Colonel Steve Warren, a Defense Department spokesman, said one lab in Britain and another in Massachusetts had been added to the list of laboratories that received live anthrax samples, raising the total number of labs to 68.

Four countries outside the United States are now known to have received live anthrax samples: Australia, Canada, South Korea and Britain. Labs in 19 states and Washington, D.C., also received live anthrax samples.

Investigators are trying to determine whether the inadvertent shipments of the anthrax, which can be used as a biological weapon, stemmed from quality control problems at the U.S. base, the Dugway Proving Ground, Pentagon officials said.