Qassem Soleimani

Updated at 5 p.m. ET

President Trump said that Iran appears "to be standing down" after Tuesday night's missile attack in Iraq and that "the American people should be extremely grateful and happy no Americans were harmed."

Trump, in a nationally televised address from the White House, also announced a new round of what he termed "punishing economic sanctions" against the Iranian government. And he called on NATO to become "much more involved in the Middle East process."

Iranian Foreign Minister Mohammad Javad Zarif tells NPR that the U.S. "will pay" for a drone strike that killed the commander of the country's elite Quds Force, which he described as an act of "both terrorism and war."

Speaking with All Things Considered host Mary Louise Kelly in Tehran, Zarif said last week's assassination of Maj. Gen. Qassem Soleimani was "a cowardly armed attack" that "amounts to war."

"[We] will respond according to our own timing and choice," he said.

Updated at 11:50 p.m. ET Sunday

As thousands of mourners flooded the streets of Iran on Sunday to mourn the death of Gen. Qassem Soleimani, a series of dizzying developments convulsed the Middle East, generating new uncertainty around everything from the future of U.S. forces in Iraq to the battle against ISIS and the effort to quell Tehran's nuclear ambitions.

Amid the fallout of the U.S. drone strike on Friday that killed Soleimani, Sunday saw the following whiplash-inducing developments unfold almost simultaneously:

Updated at 3:15 p.m.

President Trump, in his first public remarks in the wake of a U.S. strike that killed Iranian Maj. Gen. Qassem Soleimani, defended the action as necessary to protect national security.

"We took action last night to stop a war. We did not take action to start a war," Trump said Friday afternoon from his Mar-a-Lago resort in Florida.

Updated at 1:07 p.m. ET

President Trump ordered a bold strike against Iran this week that jangled the Middle East and Washington, drawing praise from allies, skepticism from critics and, most of all, questions about what comes next.

Updated at 4:27 a.m. ET Friday

U.S. forces assassinated Iranian Maj. Gen. Qassem Soleimani in an airstrike early Friday near the Baghdad International Airport, an escalation of tensions between Washington and Tehran that is prompting concerns of further violence in the region.