None by the US.
Sure the US lost nukes.
Like the 4 they lost off the coast of Spain
U.S. accidentally drops hydrogen bombs in Spain | January 17, 1966 | HISTORY
On January 17, 1966, a B-52 bomber collides with a KC-135 jet tanker over Spain’s Mediterranean coast, dropping three 70-kiloton hydrogen bombs near the town of Palomares and one in the sea. It was not the first or last accident involving American nuclear bombs. As a means of maintaining...
www.history.com
Or the one they lost in Greenland.
1968 Thule Air Base B-52 crash - Wikipedia
en.wikipedia.org
Pure luck none of them exploded.