European nations worked Monday to keep diplomatic efforts to curb the Israel-Iran war alive as the two countries traded strikes following the United States’ weekend attack on Iran’s nuclear program. Calls for Tehran to enter talks with Washington appeared to fall on deaf ears as it reached out to ally Russia for support.

F.B.I. and D.H.S. officials cautioned state and local law enforcement of the possibility of threats to U.S. communities.

Trump announced on Saturday that the United States had completed a “very successful attack” on Iran’s key nuclear facilities — including Fordo, Natanz and Isfahan — in a post on his Truth Social platform. He wrote that a “full payload of BOMBS” were dropped, and U.S. planes were safely on their way home.