Five people were wounded in the attack, including three coalition members and two Iraqi soldiers, according to spokesman for the U.S.-led coalition Myles Caggins.
Jonathan Hoffman, chief Pentagon spokesman, said later that three U.S. service members were wounded in the Camp Taji attack. Two of them were seriously wounded and are hospitalized.
He said Iraqi security forces have made an initial arrest.
Hoffman also repeated Defense Secretary Mark Esper’s comments from last week, saying, “You cannot attack and wound American service members and get away with it. We will hold them accountable.”
A statement from Iraq's military said the “brutal aggression” wounded a number of air defense personnel who remain in critical condition, but did not provide a number.
Iraqi forces later discovered seven platforms from which the rockets were in the Abu Azam area, north of Baghdad. Another 24 missiles were discovered in place and ready to launch.
The attack was unusual because it occurred during the day. Previous assaults on military bases housing U.S. troops typically occurred at night.
Iran-backed Shiite militia groups vowed to exact revenge for Friday's U.S. strikes, signalling another cycle of tit-for-tat violence between Washington and Tehran that could play out inside Iraq.
Iraq's military also cautioned the U.S. from retaliating as it did on Friday without approval from the government. Taking unilateral action would "not limit these actions, but rather nurtures them, weakens the ability of the Iraqi state,” the statement said.
Gen. Frank McKenzie, commander of the U.S. Central Command, said Friday that counterstrikes on PMF bases were intended to send a message to Kataib Hezbollah and Iran that further assaults on coalition forces would not be tolerated. If that message is ignored, the U.S. could respond with additional strikes, he told reporters.
“If it doesn't work, we got plenty more places we can go and go to work, and I'm confident we'll do that,” he said.
America's killing of Iraqi security forces might also give Iran-backed militia groups more reason to stage counterattacks against U.S. troops in Iraq, analysts said.
“We can’t forget that the PMF is a recognized entity within the Iraqi security forces; they aren’t isolated from the security forces and often are co-located on the same bases or use the same facilities,” said Sajad Jiyad, a researcher and former managing director of the Bayan Center, a Baghdad-based think tank.
“Now the (Iran-backed) groups who supported the initial strike in Taji, who were the most outspoken, feel obliged, authorized, maybe even legitimized to respond, ostensibly to protect Iraqi sovereignty but really to keep the pressure up on Americans,” he added.
“There are no red lines anymore," Jiyad said.
Wednesday's attack on Camp Taji was the deadliest to target U.S. troops in Iraq since a late December rocket attack on an Iraqi base, which killed a U.S. contractor. That attack set in motion a series of attacks that brought Iraq to the brink of war.
After the contractor was killed, America launched airstrikes targeting Kataib Hezbollah, which in turn led to protests at the U.S. Embassy in Baghdad.
A U.S. drone strike in Baghdad then killed Iranian Gen. Qassem Soleimani, a top commander responsible for expeditionary operations across the wider Mideast. Iran struck back with a ballistic missile attack on U.S. forces in Iraq, the Islamic Republic’s most direct assault on America since the 1979 seizing of the U.S. Embassy in Tehran.
The U.S. and Iran stepped back from further attacks after the Soleimani incident. A senior U.S. official said in late January, when U.S.-Iran tensions had cooled, that the killing of Americans constituted a red line that could spark more violence.