US European Command said in a statement: "During a routine air refuelling mission as part of military training, a U.S. military aircraft carrying five service members suffered a mishap and crashed into the Mediterranean Sea."

"All five of the service members onboard the aircraft were killed,"  the statement said.

Search and rescue efforts began immediately, including nearby U.S. military aircraft and ships.

The US has increased operations in the region amid the ongoing Israel-Hamas conflict.

"Our thoughts and prayers are with the families of the fallen. An investigation into the crash is underway," the statement said.

Meanwhile, US President Joe Biden mourned the loss of lives in the incident and said in a statement: "Today, Jill and I mourn the loss of 5 American service members who died when their aircraft crashed in the Mediterranean Sea during a routine training mission. Our service members put their lives on the line for our country every day."