Eighteen British soldiers wounded in Afghanistan and Iraq may have received improperly-screened blood transfusions from American stores, the British Ministry of Defence said Thursday.

The affected soldiers have all been contacted and offered the appropriate tests, ministry officials said.

"The actual risk of any infection is low — however we are taking it extremely seriously," Under Secretary of State for Defence Derek Twigg said in a release.

In emergency situations, military forces sometimes use other coalition medical facilities, blood or blood products if they are available sooner, the ministry explained on its website. If supplies are exhausted, medical officials use emergency donor panels which are later screened. 

The soldiers in question may have received blood that "might not have had a valid retrospective test," the ministry said on its website, adding there was a "small risk" the transfusion could have transferred blood-borne disease from the donor to the recipients.

The ministry said a small number of British soldiers have received U.S. blood samples in recent years.

"These 18 service personnel would almost certainly have died without receiving an emergency blood transfusion at the front line," Twigg said.

"We are working with the appropriate health authorities to do all that we can to test and reassure the people involved. We are, and will continue to do, all that we can to support them and their families through this uncertain time."

The British news agency Press Association quoted an unidentified U.S. Department of Defence spokeswoman as saying that all donors whose blood was given to British soldiers had been tested and found free of HIV and hepatitis.

"All the soldiers that received the blood have also been tested, and we are waiting for the results of those tests," the spokeswoman was quoted as saying.

With files from the Associated Press