He said that Iran, in targeting the al-Asad air base in the western Iraqi desert, "put 11 large rockets with 1,000-pound, 2,000-pound (more than 900-kg) warheads in it, but we took sufficient defensive measures."

No U.S. forces were injured by the 16 short-range ballistic missiles fired from three sites inside Iran, targeting two military bases in Iraq where U.S. armed forces are stationed. But Milley said, the absence of casualties "has more to do with the defensive techniques our forces used than it does with intent."

Pence's assessment echoed comments Wednesday from the top U.S. military leader, Joint Chiefs Chairman Gen. Mark Milley, who told reporters at the Pentagon, "The points of impact were close enough to personnel and equipment and so on and so forth. I believe, based on what I saw and what I know, is that they were intended to cause structural damage, destroy vehicles and equipment and aircraft, and to kill personnel."

The ballistic missiles fired at American bases... we believe were intended to kill Americans," Vice President Mike Pence told the NBC news network on Thursday. "We have intelligence to support that was the intention of the Iranians."

U.S. officials say they believe Iran intended to kill American forces with its ballistic missile attacks on bases in Iraq, even as President Donald Trump said Iran "appears to be standing down" from new conflict with the U.S."

Defense Secretary Mark Esper said damage at the al-Asad base was confined to "tentage, taxiways, the parking lot, a damaged helicopter, things like that. Nothing that I would describe as major. No friendly casualties, whether they're U.S., coalition, contractor."

Iran on Thursday disputed the U.S. accounts of the missile attacks and their intent. Iranian state media quoted Brig. Gen. Amir Ali Hajizadeh, head of the Revolutionary Guard's Aerospace Force, as saying, "We did not intend to kill. We intended to hit the enemy's military machinery." He repeated the Iranian government's claim that "tens of people were killed or wounded."

Trump, in a nationally televised address Wednesday from the White House, signaled the U.S. would not take military action in response to the attacks, but instead would impose additional harsh economic sanctions against Iran to further hobble its economy.

Iran fired the missiles into Iraq early Wednesday in retaliation for the Trump-ordered drone attack last week that killed Iranian Quds force commander Qassem Soleimani, whom the U.S. leader said "was responsible for some of the absolutely worst atrocities" in the Middle East.

The Democrat-controlled U.S. House of Representatives is voting Thursday to curb further attacks on Iran absent congressional approval, with a similar measure under consideration in the Republican-majority Senate. But Trump could veto any such congressional resolution, with lawmakers unlikely to muster the necessary two-thirds majority to override such a move.

House Speaker Nancy Pelosi told reporters she holds Soleimani responsible for the deaths of American armed forces. Pelosi, however, said she did not believe that in "terms of what is in the public domain" about the rationale for the Trump-ordered drone attack on Soleimani, the U.S. was made safer.

Trump has said Soleimani was planning more attacks on U.S. personnel in the Middle East, which posed an "imminent threat" to the U.S., a justification for the drone attack to kill him. But Trump officials have declined to detail specifics of the threat.

Trump, in his address, said that rather than continued conflict with Iran, the two countries could cooperate on issues of mutual concern.

The Islamic State group "is a natural enemy of Iran," Trump said. "The destruction of ISIS is good for Iran, and we should work together on this and other shared priorities."

The U.S. president told the Iranian people, "We want you to have a future, and a great future, one that you deserve. One of prosperity at home and harmony with the nations of the world. The United States is ready to embrace peace with all who seek it."

Iran's supreme leader, Ayatollah Ali Khamenei, called the Iranian strikes a "slap in the face" to the United States and said the "corrupt presence" of the U.S. in the region should come to an end.

Iranian President Hassan Rouhani added later in a tweet that Iran's "final answer" to the killing of Soleimani "will be to kick all U.S. forces out of the region."

On Thursday, Rouhani warned the U.S. against a new attack, while a senior commander vowed more retribution for the killing of Soleimani. The Iranian president said that its missile attacks on the U.S. forces in Iraq were a legitimate act of self-defense under the UN Charter, but he warned that "if the U.S. makes another mistake, it will receive a very dangerous response."

The semi-official Tasnim news agency quoted Abdollah Araghi, a member of Iran's joint chiefs of staff, as saying that the country's Revolutionary Guard "will impose a more severe revenge on the enemy in the near future."