No further details were provided.
The spokesman added that US officials are remaining in touch with their Israeli counterparts.
Earlier on Sunday, US President Joe Biden spoke with Prime Minister Benjamin Netanyahu. The President expressed deep sympathy for all those missing, wounded, and killed and pledged his full support for the Government and people of Israel in the face of an unprecedented and appalling assault by Hamas terrorists.
The two discussed the taking of hostages by Hamas terrorists, including entire families, the elderly, and young children. The President emphasized that there is no justification whatsoever for terrorism, and all countries must stand united in the face of such brutal atrocities.
President Biden updated the Prime Minister on the intensive diplomatic engagement undertaken by the United States over the last 24 hours in support of Israel. The President also conveyed that additional assistance for the Israeli Defense Forces is now on its way to Israel, with more to follow over the coming days.
The leaders also discussed ongoing efforts to ensure that no enemies of Israel believe they can or should seek advantage from the current situation.
Later on Sunday, the Defense Department announced that the US military will move Navy ships and military aircraft closer to Israel in a show of support for the Jewish state.
