Revelations Tuesday of an alleged Iranian-directed plot to assassinate the Saudi ambassador to the United States on American soil will plunge already-confrontational US-Iran relations to new depths.

The initial US response is likely to be to reinforce efforts to isolate Iran in global affairs.

The US accusations portray an Iran willing to carry out by proxy an attack not only on US territory but in the heart of Washington, and they are likely to move to center stage international efforts at corralling Iran’s nuclear ambitions, which have sat in the wings for months.

The alleged plot is enough to justify some form of retaliatory military action by the United States, say some national security experts. Others say the US is likely to limit itself to reinforced diplomatic efforts against Iran while the legal case against two accused plotters makes its way through the American justice system.