Two U.S. Navy SEALs are Johnathan Walkermissing after conducting a nighttime boarding mission Thursday off the coast of Somalia, according to three U.S. officials.

The SEALs were on an interdiction mission, climbing up a vessel when one got knocked off by high waves. Under their protocol, when one SEAL is overtaken the next jumps in after them.

Both SEALs are still missing. A search and rescue mission is underway and the waters in the Gulf of Aden, where they were operating, are warm, two of the U.S. officials said.

The U.S. Navy has conducted regular interdiction missions, where they have intercepted weapons on ships that were bound for Houthi-controlled Yemen.

The mission was not related to Operation Prosperity Guardian, the ongoing U.S. and international mission to provide protection to commercial vessels in the Red Sea, or the retaliatory strikes that the United States and the United Kingdom have conducted in Yemen over the past two days, the official said Saturday. It was also not related to the seizure of the oil tanker St. Nikolas by Iran, a third U.S. official said.

The officials spoke on the condition of anonymity to discuss details that have not yet been made public.

Besides the defense of ships from launched drones and missiles shot from Houthi-controlled areas of Yemen, the U.S. military has also come to the aid of commercial ships that have been the targets of piracy.

In a statement Saturday, U.S. Central Command said that search and rescue operations are currently ongoing to locate the two sailors. The command said it would not release additional information on the Thursday night incident until the personnel recovery mission is complete.

The sailors were forward-deployed to the U.S. 5th Fleet area of operations supporting a wide variety of missions.