Trump addresses nation, de-escalates crisis over Iran's missile attacks The president threatened new sanctions but not immediate military retaliation.

President Donald Trump addressed the nation Wednesday hours after Iran launched missile strikes on two bases in Iraq where U.S. forces were stationed, de-escalating the crisis by threatening additional "punishing" sanctions on Iran but not immediate military retaliation.

"Iran appears to be standing down which is a good thing for all parties concerned," Trump said, as Vice President Mike Pence, Secretary of State Mike Pompeo, Defense Secretary Mark Esper and the Joint Chiefs stood behind him.

"I'm pleased to inform you the American people should be extremely grateful and happy," he said. "No Americans were harmed in last night's attack by the Iranian regime."

Only minimal damage was sustained, he said, thanks to "an early warning system that worked very well."

Saying Iran will not be allowed to get a nuclear weapon, Trump struck a conciliatory tone about new negotiations over a nuclear deal, saying, "we must all work together toward making a deal with Iran that makes the world a safer and more peaceful place."

He ended by saying "the United States is ready to embrace peace with all who seek it."

The president spoke after Iran's supreme leader said his country's missile strikes had "slapped" the U.S.

Here is how the day after the missile strikes unfolded.

4:02 p.m. Senate Democrats say classified briefings showed no 'imminent threat'

Senate Democrats emerge from the closed-door briefings by Pompeo and the other top administration officials saying there was no showing of an "imminent threat" that justified last week's killing of Iran's top general. That military strike triggering Iran's missile strikes against U.S. forces in Iraq Tuesday night.

"I was deeply surprised at the lack of information" presented of a "specific, imminent threat," said Sen. Chris Murphy of Connecticut.

"It's not what I consider to be an imminent threat," said Democratic Sen. Tim Kaine of Virginia, who, like Murphy, is a member of the Senate Foreign Relations Committee.

All the Democrats complained that the briefing was too short. It was just 75 minutes long and only 15 of the 97 senators got to ask questions said Senate Minority Leader Chuck Schumer. “The questions began to get tough, and they walked out,” Schumer said.

"I came away from this briefing really angry," said Sen. Richard Blumenthal of Connecticut, a members of the Senate Armed Services Committee. "It raised more questions than it answered."

GOP Sen. Mike Lee of Utah also complained, calling the briefing "unacceptable" and "insulting."

Other Republicans, though, told reporters the briefing left them more than satisfied that the administration had made its case. "It was very well done," said Florida Republican Sen. Marco Rubio.

"One of the best briefings I've ever had," said Sen. James Risch of Idaho, the GOP chairman of the Senate Foreign Relations Committee. He called the intelligence "crystal clear."

He said polarized politics in Washington had turned such bipartisan briefings into partisan affairs.

2:50 p.m. Pompeo, Esper, Haspel, Milley briefing all members of Congress

Secretary of State Mike Pompeo, Defense Secretary Mark Esper, CIA Director Gina Haspel and Joint Chiefs Chairman Gen.Mark Milley are on Capitol Hill briefing all members of the House and Senate on Iran.

The closed-door briefings, originally scheduled to explain to members the intelligence the administration says justifies the killing of Iran's top general, Qassam Soleimani, are now expected to cover the Iranian missile strikes Tuesday night as well.

President Trump and his top officials contend Soleimani was behind what they called an "imminent threat" of attacks on U.S. diplomats and military personnel. Democrats have questioned whether that's the case, with House Speaker Nancy Pelosi calling the strike on him "dangerous" and unnecessarily "provocative."

After the top officials briefed House members, they were headed to the Senate and some members are expected to speak afterward.

1:42 p.m. New details on Iranian missiles and damage

ABC's Elizabeth McLaughlin reports from the Pentagon that, according to a U.S. official, the U.S. now believes that Iran fired between 20 and 24 short-range and medium-range missiles into Iraq.

This would be in line with the Iraqis saying 22 missiles were fired.

There were 15 missile impacts at the Al Asad base, where some structures were hit, and a couple of missiles that hit near Irbil in the Kurdistan region of northern Iraq, the official says.

1:04 p.m. Trump talks Iran with UK's Boris Johnson

President Trump spoke with the UK's Boris Johnson, the White House says in a new readout. reports ABC News' Jordyn Phelps.

"Today, President Donald J. Trump spoke with Prime Minister Boris Johnson of the United Kingdom. The two leaders discussed the current situation in the Middle East and agreed to continue close coordination in support of shared national security interests," according to the White House.

In his address today, President Trump called on the UK and other signatories of the Iran nuclear deal to abandon it in favor of seeking a new agreement.

12:50 p.m. Positive reaction from Republicans and Democrats

ABC News' Mariam Khan on Capitol Hill reports there's bipartisan praise for the president.

“A homerun speech by President Trump about the challenges we face with Iran. It was measured and firm. To the Iranian people: President Trump laid out a pathway forward for peace and prosperity. I hope you take it," GOP Sen. Lindsey Graham said in a statement. The day before, he struck a much harsher tone, saying, "Let me say tonight, if you are watching television in Iran: I just got off the phone with the president ...You continue this crap you’re going to wake up one day out of the oil business."

“I am pleased to see that both the United States and Iran are looking to avoid further escalation. I don’t believe either nation seeks open conflict," Sen Dianne Feinstein said. “War with Iran and its proxies is not the answer. I urge Iran to accept President Trump’s offer of dialogue and to work with us on shared objectives. This is the time for diplomacy. Anything else doesn’t make sense."

“Now is the time to work with our partners in the region and in Europe on a more comprehensive approach towards de-escalation – one that does not repeat the mistakes of the Obama administration, and which focuses on ending all aspects of Iran’s malign behavior, including their use of ballistic missiles, terrorism, and their nuclear program, through diplomacy,” Sen,. James Inhofe, the Republican chairman of the Senate Armed Services Committee, said.

"I applaud the president for deescalating the situation and putting us back on the path of diplomacy. We do not seek conflict, but the United States will not be deterred from protecting American lives and our vital national security interests." Sen. James Risch, the GOP chairman of the Senate Foreign Relations Committee, said in a statement.

12:18 p.m. British foreign secretary lands in Washington to meet with Pompeo

British Foreign Secretary Dominic Raab tweeted Wednesday afternoon that he had landed in Washington for “a day of valuable talks with senior members of Congress” ahead of a meeting with Secretary of State Mike Pompeo.

“A chance to discuss the importance of the UK/US security partnership and the need to de-escalate the situation in Iraq,” the tweet read.

11:40 a.m. ABC's Raddatz reports if no US attacks, Iran will not take more military action

Following the president's remarks, ABC Chief Global Affairs Correspondent Martha Raddatz, reporting from Tehran, says, "The Iranians -- the Foreign Minister -- told me that if they do not attack again, if the United States does not take military action, Iran will not either."

"Iranian officials had to know that they would be ending up in a huge conflict if they made a very, very massive attack somewhere, so they walked that line very well," Raddatz said. "They appeased the people here in so many ways, taking out some sort of retaliatory attack, but no loss of life and no larger conflict."

11:28 a.m. Trump calls for sanctions but no military action

Trump announced that the U.S. would be imposing "powerful" economic sanctions against Iran, but refrained from any immediate threats of military action against the Iranian regime even though he had said he would strike back if Iran attacked the U.S.

"As we continue to evaluate options in response to Iranian aggression, the United States will immediately impose additional punishing economic sanctions on the Iranian regime," Trump said. "These powerful sanctions will remain until Iran changes its behavior."

He added, "Our great American forces are prepared for anything. Iran appears to be standing down, which is a good thing for all parties concerned and a very good thing for the world."

10:51 a.m. House Republican Leader says clear president had to take action

ABC News' Allison Pecorin reports that House Republican leaders fully support President Trump's decision to kill the Iranian general and back the president's foreign policy judgment.

"Under this administration the strength of our foreign policy has made us safer, stronger and more respected around the globe," Minority Leader Kevin McCarthy says. "It's very clear the president had to take action."

Minority Whip Steve Scalise adds, "It was the right thing to do when President Trump gave the command to take out Soleimani," Scalise said. "We are a safer world because a brutal terrorist has been removed from the planet."

10:29 a.m. GOP chairman says Trump told him he stands ready to de-escalate

Senate Armed Services Chairman James Inhofe tells ABC News' Mariam Khan that he spoke with President Trump Tuesday night about 9 p.m. following Iran’s missile attacks which targeted U.S. forces in Iraq.

During the conversation, Inhofe says Trump told him that, based on the fact that there were no U.S. casualties, he stands ready to de-escalate the situation and negotiate with Iran going forward.

“This is going to open the door for negotiations,” Inhofe says. “I think he is taking it as an opportunity to not just de-escalate but start negotiations.”

Republican Inhofe describes the president’s mood as “very, very positive.”

Asked if Trump intends to make this clear in his expected speech this morning, Inhofe says he wouldn’t speak for the president.

At the same time, a source tells ABC News' Elizabeth McLaughlin that several key Republican senators spoke to President Trump last night about the need not to respond militarily as it appears that Iran was deliberately trying to avoid U.S. casualties with their attack.

The senators recommended conciliatory language, the source says.

10:26 a.m. McConnell warns of Iran threat, Schumer calls Trump foreign policy 'impulsive'

Senate Majority Leader Mitch McConnell speaks on the Senate floor about the Iranian missile attack on U.S. forces.

“We must remain vigilant in the face of serious threats posed by Tehran. Apparently, these strikes did not kill or wound Americans, but they demonstrate the significant progress Iran has made over the last decade in building a large, long-range, and accurate ballistic missile force,” McConnell says.

Senate Minority Leader Chuck Schumer speaks after McConnell and also condemns the Iranian attacks.

At the same time, he says, "the American people do not want a war with Iran," adding Trump did not have the authority to pursue one.

"Will more [troops] be deployed in the weeks and months ahead?" Schumer asks. "The American people rightfully have serious concerns about war with Iran, and whether we are safer today due to this president's foreign policy, which is so often impulsive and erratic. I'm afraid that these impulsive and erratic actions throughout the world are making us less safe."

Democratic Sen. Tammy Duckworth is even tougher criticizing Trump's response to the Iranian missile strikes: "Let me make something clear to Donald Trump: all is certainly not well when war is on the horizon just because you wanted to look like the toughest kid on the playground," she said.

“Like a child who is blind to consequences, ignorant of his own ignorance, he's given Iran everything they could have asked for in the end, making it far more likely that tomorrow or next week or next month more Americans will be sent into another one of the forever wars he's bragged that he, and he alone, would be able to end,” she said.

10:08 a.m. Official says Trump has met with his national security team

ABC's Jordyn Phelps reports from the White House that a senior administration official confirms the president met with members of his national security team this morning in the Situation Room.

9:31 a.m. Pence will attend the president's speech

The White House released an updated schedule for Vice President Mike Pence Wednesday morning, adding that he will join President Trump in the Grand Foyer of the White House for his 11 a.m. remarks.

9:14 a.m. White House confirms Trump will speak at 11 a.m.

The White House released an updated schedule for the President Wednesday morning, adding that Trump will address the nation at 11 a.m. from the Grand Foyer of the White House, following an attack by Iran overnight on two bases in Iraq where U.S. troops are stationed.

Earlier Wednesday, Iran's Supreme Leader Ayatollah Ali Khamenei said his country "slapped" the United States "on the face last night," referring to the missile strikes against U.S. military forces in Iraq in retaliation for the killing of Iran's most powerful commander.

"But military action is not enough," Khamenei said in a national televised address in Tehran on Wednesday, adding that the “corrupt presence of the U.S. in the region should come to an end." His speech was followed by chants from the crowd, saying, "death to America."

Iran fired more than a dozen ballistic missiles into neighboring Iraq around 2 a.m. local time on Wednesday, targeting Iraqi military bases housing American troops and coalition forces, according to Pentagon spokesman Jonathan Hoffman.

"These bases have been on high alert due to indications that the Iranian regime planned to attack our forces and interests in the region," Hoffman said in a statement, noting that "we are working on initial battle damage assessments."

"As we evaluate the situation and our response," he added, "we will take all necessary measures to protect and defend U.S. personnel, partners and allies in the region."

Iraqi Prime Minister Adil Abdul Mahdi said in a statement that his office received “an official verbal message” from Iran shortly before midnight on Wednesday that the missile strikes would begin soon and would be limited to the whereabouts of U.S. forces, without specifying locations.

A U.S. defense official told ABC News that 10 of the missiles struck the Ain al-Asad air base in western Iraq's Anbar province and one hit a base in Erbil in Iraq's semiautonomous Kurdish region. Four other missiles "failed in flight," the official said.

A source within the Kurdistan Regional Government told ABC News that three missiles were fired at Erbil International Airport and the nearby U.S.military base. Two of the rockets were shot down by anti-missile batteries while the third fell behind the airport but didn't explode, the source said.

The Islamic Revolutionary Guard Corps, a branch of the Iranian Armed Forces, swiftly claimed responsibility for the strikes as throngs of people took to the streets of Tehran to celebrate.

"We warn the Great Satan, the arrogant American regime, that any new invasions and aggression will result in more painful and pounding responses," the Islamic Revolutionary Guard Corps said in a statement.

Later, Iranian Foreign Minister Mohammad Javad Zarif wrote on Twitter that his country took "proportionate measures in self-defense Article 51 of" the Charter of the United Nations.

"We do not seek escalation or war, but will defend ourselves against any aggression," Zarif said.

Meanwhile, Iranian Minister of Information and Communications Technology Mohammad-Javad Azari Jahromi tweeted, "Get the hell out of our region!"

A U.S. official and a senior Trump administration official told ABC News that early indications are there were no American casualties from the strikes. According to U.S. sources, the troops were in bunkers at the time of the attacks.

U.S. President Donald Trump took to Twitter late Tuesday night to assure Americans that "all is well."

"So far, so good!" he tweeted. "We have the most powerful and well equipped military anywhere in the world, by far!"

Iraq's prime minister also said they haven't received any reports of Iraqi casualties so far. In a statement posted to social media Wednesday, Abdul Mahdi urged both sides to "not engage in open warfare" and "to exercise restraint."

Amid the escalating tensions, a growing number of international air carriers have decided to suspend or reroute flights to avoid the airspace over Iran and Iraq.

The attacks occurred just hours after Iran's foreign minister told ABC News that the United States "will pay" for the death of Maj. Gen. Qassem Soleimani, longtime leader of the elite Quds Force in Iran's Islamic Revolutionary Guard Corps.

Officials with the U.S. Department of Defense have confirmed that Trump ordered the airstrike that killed Soleimani near Baghdad International Airport on Jan. 2.

Over the past 20 years, Soleimani had led the Quds Force in operations throughout the region, backing Syrian President Bashar al-Assad and supporting Shiite militia groups in Iraq, including against U.S. troops during the Iraq War. The U.S. Department of State said Soleimani's forces are responsible for the deaths of hundreds of American troops because of the kind of explosive devices they helped bring to Iraq. The United States designated Soleimani a terrorist in 2011 under then-President Barack Obama.

The Trump administration has argued that Soleimani's death was critical to foiling "imminent attacks" that the Iranian commander was helping to plot against U.S. personnel in the region. The administration has provided no evidence of those plans.

On the weekend after the U.S. airstrike, the Iranian government announced it will no longer abide by any of the operational restraints on its nuclear program under the deal, from which the Trump administration withdrew the United States in May 2018.

Hundreds of thousands of people have taken to the streets of Tehran and other cities across Iran in recent days to mourn Soleimani and show support for the Iranian government. The massive crowds have voiced anger at the U.S. airstrike and have hailed the slain general as a national hero.

ABC News' Conor Finnegan, Ben Gittleson, Luis Martinez, Matt McGarry, Elizabeth McLaughlin, Martha Raddatz, Kirit Radia, Cindy Smith and Anne Flaherty contributed to this report.