Four Americans, including a couple from Southern California, who were taken hostage by Somali pirates were fatally wounded by their captors while negotiations between the pirates and U.S. military forces were under way in the Gulf of Aden, U.S. Central Command said Tuesday.

The four were aboard the vessel Quest, which was captured last week.

“”We express our deepest condolences for the innocent lives callously lost aboard the Quest,”” said Marine Gen. James N. Mattis, commander of Central Command.

Four U.S. Navy ships had been shadowing the Quest after it was taken over by the pirates, Mattis said. While negotiations were under way to gain the release of the Americans, U.S. forces responded to gunfire aboard the Quest. The four Americans had been shot, Mattis said.

Two of the pirates were killed by U.S. forces and 13 captured, Mattis said. After boarding the Quest, military personnel found the bodies of two other pirates. The incident occurred about 1 a.m. EST.

“”Despite immediate steps to provide lifesaving care, all four hostages ultimately died of their wounds,”” according to a statement from Central Command.

The four Americans also included a couple from the Seattle area.