At the White House on Friday, Secretary of State Mike Pompeo, left, and Treasury Secretary Steven Mnuchin brief reporters about additional sanctions placed on Iran. Evan Vucci/Associated Press

WASHINGTON — Confronted by persistent questions about his military action in the Middle East, President Trump and his top officials offered a string of fresh explanations Friday, with Trump now contending Iranian militants had planned major attacks on four U.S. embassies.

Just hours earlier, Secretary of State Mike Pompeo had said the U.S. didn’t know when or where attacks might occur. Trump and other officials insisted anew that Iranian Gen. Qassem Soleimani had posed an imminent threat to the U.S., but they rebuffed repeated attempts to explain what they meant by “imminent.”

Trump, meanwhile, announced additional sanctions against Iran, which he had promised after a barrage of missiles fired by the Islamic State against American bases in Iraq earlier this week.

Those Iranian missiles, which caused no casualties, were prompted by the U.S. drone strike that killed Gen. Qassem Soleimani last week in Baghdad. That U.S. assault set off a chain of events that may have included the downing of a Ukrainian jetliner, possibly by an Iranian missile, and calls by the Iraqi government to expel U.S. troops from their country.

At the White House, Trump issued an executive order adding additional U.S. sanctions to the already long list his administration had imposed in an effort to force Iran to accept a new agreement that would curb its nuclear program and to halt support for militant groups throughout the Middle East.

Trump declared the U.S. was holding Iran responsible for attacks against the United States as well as a threat to U.S. service members, diplomats and civilians – an apparent reference to the justification for killing Soleimani.

“The United States will continue to counter the Iranian regime’s destructive and destabilizing behavior,” he said.

But Trump and others faced continuing questions over their claims of an “imminent” threat. Members of Congress said Pompeo and other officials did not provide sufficient detail or justification in briefings this week.

Define what you mean by imminent, Pompeo was asked Friday at a White House news conference.

“I don’t know exactly which minute,” Pompeo said. “We don’t know exactly which day it would have been executed, but it was very clear. Qassem Soleimani himself was plotting a broad, large-scale attack against American interests and those attacks were imminent.”

Both Pompeo and Trump had said U.S. embassies were threatened. The secretary of state broadened it to include “American facilities,” including military bases throughout the region. “This was going to happen, and American lives were at risk,” he said.

Trump gave a more worrisome number but still no specifics in a later comment.

“I can reveal that I believe it probably would’ve been four embassies,” he told Fox News in an interview taped Friday.

He spoke amid revelations by U.S. officials that the American military had tried, but failed, to kill another senior Iranian commander on the same day that Soleimani was killed. The targeting of Abdul Reza Shahlai was apparently part of an effort to cripple the leadership of Iran’s Quds Force, which the U.S. has designated a terror organization along with the larger Islamic Revolutionary Guard Force.

House Speaker Nancy Pelosi called the killing of Soleimani “provocative and disproportionate,” and other members said they were unconvinced after a closed-door briefing on the intelligence.

“President Trump recklessly assassinated Qasem Soleimani,” said Rep. Pramila Jayapal, a Washington state Democrat. “He had no evidence of an imminent threat or attack.”

The new sanctions were in immediate response to Iran’s firing of a barrage of missiles at American bases in neighboring Iraq this week after the killing of Soleimani. No one was injured. The larger U.S. goal is to force Iran to negotiate a new agreement on limiting its nuclear program.

In 2018, Trump withdrew from the nuclear agreement signed under President Barack Obama that traded curbs on the program for the easing of sanctions. Since then, the administration has added additional economic measures that have created hardship in Iran and brought its oil revenue to historic lows but have failed to bring the Iranian government to the negotiating table.

The sanctions added Friday include measures aimed at eight senior Iranian officials involved in what Treasury Secretary Steven Mnuchin called “destabilizing” activities throughout the Middle East as well as Tuesday’s missile barrage.

Those measures, which would freeze any assets the officials have in U.S. jurisdiction and prohibit financial transactions with them, are largely symbolic since such senior figures are unlikely to have assets under American control after decades of hostility between the two nations.

But other measures announced Friday could have a significant effect on strategically important sectors of the Iranian economy, said Ben Davis, chief research officer at research and data analytics firm Kharon.

The executive order grants the administration power to place anyone involved, even indirectly, in the construction, manufacturing, textile or mining sector on a global financial blacklist. It also targets 17 of the largest steel and iron manufacturers – one of the few growth spots in the hobbled Iranian economy – along with three foreign companies, including two based in China, under secondary sanctions.

“It sends a signal to other foreign firms that continue to do business with Iranian steel producers that this is off limits,” said Davis, a former Treasury Department official.

Adnan Mazarei, a senior fellow at the Peterson Institute for International Economics, said the sanctions will hurt an Iranian economy that was forced to cut fuel subsidies earlier this year, triggering nationwide protests, but they also will make it harder for government to negotiate with the U.S.

“This will be seen as another sign that the U.S. government cannot be taken at its word when it says it wants to negotiate,” Mazarei said.

Mnuchin insisted the sanctions are working and have deprived Iran of tens of billions of dollars. “They would be using that for terrorist activities throughout the region and to enable them to do more bad things,” he said. “And there’s no question, by cutting off the economics to the region, we are having an impact.”