(Reuters) - Several U.S. nationals have died since the start of Hamas' surprise attack on Israel on Saturday, a National Security Council spokesman said Sunday, adding that U.S. officials remained in touch with their Israeli counterparts.

Official word of Americans killed in the conflict came as Israel retaliated for the incursion, one of the bloodiest in it history, launching attacks on the Palestinian enclave of Gaza.

(Reporting by Steve A Holland in Washington; Editing by Kim Coghill)