U.S. and Italian aircraft on Monday searched the Adriatic Sea after losing contact with a U.S. fighter jet believed to have crashed during a training mission off the coast of Italy.

The headquarters of the 31st Fighter Wing, at Aviano Air Base in Italy, said in a statement that the F-16 fighter had one pilot aboard when contact was lost Monday evening.

There was no early word on the fate of the plane or the pilot.

"The search for and rescue of our pilot is our top priority," said Col. David W. Walker, 31st operations group commander at Aviano. "We want to assure the family and friends of the lost airman that we are doing everything we can for this effort."

Initial word was that the F-16, which had taken off from Aviano, was not carrying weapons.

Italian aircraft and boats were helping in the search. The paramilitary Carabinieri force deployed helicopters, the Italian coast guard had motorboats in the area and Italian air force helicopters were also involved.

The search was focused on waters off a roughly a 9.5-mile stretch of coast between Cervia and Cesenatico in the northwestern end of the Adriatic.

Italian news agency LaPresse said the F-16 had sent an alarm signal to Aviano before it disappeared, and that three other F-16s that were flying in the same training mission made it safely back to Aviano base.

Weather conditions were difficult.

"The visibility is already poor because it is night, but there is also sleet" in the area hampering visibility, said Italian Coast Guard Cmdr. Cosimo Nicastro. The coast guard asked three commercial cargo ships in the area to help out. The area of sea where the search was being concentrated was approximately 10 miles off the coast, Nicastro said.

An Italian coast guard plane was also involved in the search mission, along with its rescue boats.