The U.S. Forces Korea will step up transparency in running biological defense programs in South Korea, the USFK said Thursday, as the allies expand their probe into the live anthrax shipment to a U.S. base here.

Earlier in the day, the joint South Korea-U.S. team in charge of investigating the shipment conducted an on-site inspection of Osan Air Base, where a sample of live anthrax spores was inadvertently shipped.

It was the first investigation by the joint working group at the base since the Pentagon announced in May that live samples of the lethal bacterium were sent from a U.S. military laboratory to laboratories in nine U.S. states and the American military base in South Korea.

A U.S. probe confirmed later that 86 American and foreign labs had received the anthrax spores, which were not completely inactive.

"This joint working group will continue to ensure reliability and transparency of the ROK-U.S. capabilities to defend the Republic of Korea," USFK Maj. Gen. Robert Hedelund, who heads the U.S. side of the joint team, said of the base inspection.

He vowed the joint working group's continued investigative efforts, saying, "I am confident that this JWG will build on the progress we have made as an alliance since the date of the incident."

The sample was brought in as part of the USFK's regular training exercises against biochemical weapons, called JUPITR, amid growing threats from North Korea's biochemical weapons.

The allies will work together to review the biological defense programs "to ensure these programs continue in a safe and effective manner," the USFK said in a statement.

The focus of Thursday's inspection was on the procedures for the sample's shipment and its disposal, as well as the Osan lab's anti-biochemical weapons tests, according to a Defense Ministry official.

The joint team also reportedly collected samples from the lab's facilities to see if there's any residue of the live anthrax spores, he added.

South Korean head of the team, Army Maj. Gen. Jang Kyung-soo, said the JWG will review the background and after measures of the incident, vowing to "come up with measures that could prevent a recurrence of any similar incident in this sort."

A total of 22 civilian and military personnel "may have been exposed," but they were given emergency treatment, and none showed any symptoms of anthrax afterward, the USFK said earlier.

The sample was destroyed upon notification from the U.S. Department of Defense, it said. (Yonhap)