Oman and Qatar were leading efforts to begin ceasefire talks, while mediators said Iran was open to resuming nuclear negotiations if Israel’s attacks stop.

Iran has vowed to retaliate against the U.S., too, while Trump has warned: “If we are attacked in any way, shape, or form by Iran, the full strength and might of the U.S. Armed Forces will come down on you at levels never seen before.” Here’s what to know about U.S. involvement so far.

Iran has told mediators Qatar and Oman that it is not open to negotiating a ceasefire while it is under Israeli attack, an official briefed on the communications told Reuters on Sunday, as the two foes launched fresh attacks and raised fears of a wider conflict.