A US Air Force investigation concluded that "most sites" used for deploying nuclear weapons in Europe lack the minimum security requirements of the US Department of Defence, according to the Federation of American Scientists that pushed for release of details of the report.
A summary of the report was released in February, but declassified details obtained by the federation reveal "a much bigger nuclear security problem in Europe" than was previously known, the group wrote on its website.
As a consequence, the US military plans to withdraw its nuclear custodial unit from one base and possibly consolidate remaining sites into fewer bases, reported dpa.
The European bases in question are places where nuclear weapons are stored for possible use by the host country's own aircraft.
US nuclear weapons are stored in underground vaults at bases in Belgium, Germany, Holland, Italy, Turkey and the United Kingdom, the federation said, mostly at US Air Force bases.
Belgium, Germany, Holland and Italy each have nuclear weapons at one of their national air bases.
The weapons at each of the national bases are under control of the US Air Force in peacetime but would, upon receipt of proper authority from the US National Command Authority, be handed over to the national Air Force at the base in a war for delivery by the host nation's own aircraft, the federation wrote.
The Blue Ribbon Review (BRR) was carried out after the US Air Force lost track of six nuclear warheads for more than a day last year as they were flown across the US.
The BRR found that "host nation security at overseas nuclear- capable units varies from country to country in terms of personnel, facilities, and equipment," the federation quoted the report as saying.
There were security lapses in "support buildings, fencing, lighting, and security systems," the report found.
One example cited was putting conscripts with as little as nine months active duty to protect nuclear weapons against theft.
The number and location of nuclear weapons in Europe are secret, but the federation estimated the number at 200 to 350 B61 nuclear bombs.