A U.S. F-16 fighter jet may have crashed on Monday during a training exercise over the Adriatic Sea and the U.S. Air Force said the status of its Italy-based pilot was unknown.
Search efforts, aided by Italy's Coast Guard, were under way and the Air Force declined to offer many details.
It said only that it "lost contact" with the F-16 at about 8 p.m. local (2100 GMT) - language often used to describe a possible crash, although Air Force officials declined to speculate about the incident.
"The aircraft was performing a training mission over the Adriatic Sea with one person on board. The pilot's condition is unknown at this time," the Air Force said in a statement.
Italy's Coast Guard confirmed it was helping in the search-and-rescue effort.
A spokeswoman at Aviano Air Base in northern Italy said more information would released as it became available.