Iran attacked at least two bases in Iraq that house American military forces on Wednesday morning local time, Iranian and U.S. officials said.

It launched ballistic missiles in its first move against the U.S. since President Donald Trump ordered an American drone strike to kill Iranian Gen. Qassem Soleimani, dramatically escalating tensions between the two countries. The offensive did not cause any casualties among American or Iraqi forces, AP reported Wednesday.

Iran’s Islamic Revolutionary Guard Corps (IRGC) — the branch of the country’s military in which Soleimani served — directed the assault, it told Iranian and American media.

“The brave soldiers of IRGC’s aerospace unit have launched a successful attack with tens of ballistic missiles on Al Assad military base in the name of martyr Gen. [Qassem] Soleimani,” read an IRGC statement sent to New York Times reporter Farnaz Fassihi.

The Iranians targeted al-Asad airbase and a base in Erbil in Iraq’s semi-autonomous Kurdish region, Pentagon spokesman Jonathan Hoffman said in an emailed statement to journalists.

“We are working on initial battle damage assessments,” Hoffman added. “As we evaluate the situation and our response, we will take all necessary measures to protect and defend U.S. personnel, partners, and allies in the region.”

Trump monitored the situation, White House press secretary Stephanie Grisham said.

Tehran launched 15 missiles, four of which failed in flight, a defense official told the Los Angeles Times. U.S. radar detected those targeted at al-Asad, which meant soldiers there could take cover.

More than 5,000 American troops are in Iraq as part of the effort to fight the self-described Islamic State. The country shares a long border with Iran, and Tehran has broad influence there through a network of allied militias and politicians. Soleimani’s killing made an Iranian response inevitable and put U.S. citizens and interests at risk, the Trump administration and analysts said. U.S. and Iraqi officials said this week that they were preparing for the movement of American forces out of Iraq ― a prospect that achieves one of Iran’s top goals and is a boon for ISIS as it attempts to regroup.

How the Wednesday attack affects the chances of further U.S.-Iran confrontation isn’t immediately clear.

Both Trump and Iranian Foreign Minister Javad Zarif appeared not to be pushing for immediate escalation.

“All is well! Missiles launched from Iran at two military bases located in Iraq. Assessment of casualties & damages taking place now. So far, so good!” Trump tweeted Tuesday evening. “We have the most powerful and well equipped military anywhere in the world, by far! I will be making a statement tomorrow morning.”

Zarif described Tuesday’s missile strikes as “proportionate measures in self-defense.” Iran does “not seek escalation of war, but will defend ourselves against any aggression,” he wrote on Twitter.

“This may be a big deal or it may be a symbolic way to launch some [initial] retaliatory strikes that are easy to execute without that much damage,” Ilan Goldenberg, a former State and Defense Department official now with the Center for a New American Security, wrote on Twitter. “We need to wait and see.”

The IRGC said it intends to retaliate against U.S. allies if they allow further American attacks on Iran to be launched from their countries, Fassihi reported. That’s a worrying prospect for a range of nations, including Qatar, Bahrain, the United Arab Emirates and even Turkey. Regional officials, including from Iran’s chief rival Saudi Arabia, have loudly been saying they want to see tensions reduced and are not eager for an outright and broad conflict.

Lawmakers have also urged restraint and plan to soon consider legislation they hope will limit Trump’s ability to strike Iran.

Beyond the American forces in Iraq, there are more than 50,000 other U.S. personnel in parts of the Middle East within Iran’s reach as well as up to 13,000 in neighboring Afghanistan, where Soleimani’s successor in the Iranian military has operated for years. That’s in addition to tens of thousands of American diplomats and private citizens.

The facilities hosting Americans house far more members of the Iraqi military working alongside them. Wednesday’s attacks killed some Iraqis, CNN reported.

The U.S. military did not immediately respond to a HuffPost request for comment.

This article has been updated with comments from Trump and Iran’s foreign minister.

Jessica Schulberg contributed to this article.