• The Pentagon released footage of retaliatory U.S. airstrikes in Iraq and Syria against facilities used by Iran-backed militia groups.
• The strikes come as the Biden administration works to revive the Iran nuclear deal.
• Iraq's military issued a rare condemnation, calling the U.S. strikes a "blatant and unacceptable violation of Iraqi sovereignty and national security."

The Pentagon on Monday released footage of retaliatory U.S. airstrikes in Iraq and Syria against facilities used by Iran-backed militia groups, a move expected to rattle the fragile diplomatic overtures surrounding the revival of the 2015 Iranian nuclear deal. 

The Biden administration said Sunday's "defensive precision airstrikes" targeted weapons storage facilities in Syria and another location in Iraq.

"The targets were selected because these facilities are utilized by Iran-backed militias that are engaged in unmanned aerial vehicle attacks against U.S. personnel and facilities in Iraq," Pentagon spokesman John Kirby wrote in an evening statement.

Iraq's military issued a rare condemnation, calling the U.S. strikes a "blatant and unacceptable violation of Iraqi sovereignty and national security."

White House press secretary Jen Psaki said Monday that the Biden administration notified allies in the region and consulted with congressional members ahead of the airstrikes.

Sunday's strikes were the second time President Joe Biden has ordered a U.S. military response in the region against Iranian-backed militia groups.

In February, the U.S. launched airstrikes against multiple facilities in Syria used by a number of Iranian-backed proxies, including Kata'ib Hezbollah and Kata'ib Sayyid al-Shuhada. The U.S. airstrikes came a week after a rocket attack in northern Iraq killed one civilian contractor and injured nine others, including a U.S. service member.

Unlike the February strike, though, Sunday's action targeted infrastructure in both Iraq and in Syria.

'Unambiguous deterrent'

Secretary of State Antony Blinken described Sunday's attacks as a "necessary appropriate deliberate action" after meeting with representatives of the Defeat-ISIS Coalition Ministerial in Rome to discuss the ongoing crisis in Syria.

"We have been very clear, the president has been very clear throughout that we will act to protect U.S. personnel and given these ongoing attacks by Iran-backed groups, targeting our interests in Iraq, he directed further military action," Blinken said alongside Italian foreign minister Luigi Di Maio.

"We took necessary appropriate deliberate action that is designed to limit the risk of escalation but also to send a clear and unambiguous deterrent message," Blinken added.

Foreign policy experts said the latest airstrikes raise questions as to why the U.S. military still maintains a footprint in Iraq and Syria.

"We will always defend U.S. troops deployed to war zones, but the extended presence in Iraq and Syria risks escalation to wider war with local militias — and even with Iran," wrote Defense Priorities Policy Director Benjamin Friedman.

"Militia groups, let alone hostile states, are getting better at precisely targeting missiles and using drones, and defensive measures are getting more difficult — this shift is one reason among many to radically reduce the U.S. troop presence in the Middle East," he added.

Randa Slim, director of Conflict Resolution and Track II Dialogues Program at the Middle East Institute, said that since March, Iran-backed militias have mounted at least 10 explosive-laden drone attacks on U.S. and coalition sites in Iraq.

"While pressure has been building from congressional leaders for the Biden administration to retaliate against drone attacks on U.S. forces in Iraq, this attack raises the specter of whether or not the U.S. is being dragged into an escalatory spiral with Iran in the Middle East, at a time the administration is scaling back its military footprint in the region," Slim, a non-resident fellow at SAIS Hopkins Foreign Policy Institute, wrote in an email to CNBC.

The strikes come as the Biden administration carries out the herculean task of withdrawing U.S. troops from Afghanistan, revaluates its foreign policy interests in the Middle East and works to revive a nuclear deal with Iran and world powers.

"The Biden administration is trying not to encourage further attacks on American forces, but they also don't want to escalate the situation," Stephen Biddle, adjunct senior fellow for defense policy at the Council on Foreign Relations and professor of international and public affairs at Columbia University, told CNBC.

"There are plenty of options for doing more than what the administration decided to do, they chose not to. So, I think what that indicates is that they're trying to manage this," Biddle said, adding that an escalation could dissolve the JCPOA negotiations and drag the U.S. into another conflict in the Middle East.

"Like it or not, the general state of U.S.-Iranian relations is going to affect the JCPOA negotiations," Biddle added.

Brokered by the Obama administration, the 2015 Joint Comprehensive Plan of Action, or JCPOA, lifted sanctions on Iran that had crippled its economy and cut its oil exports roughly in half. In exchange for billions of dollars in sanctions relief, Iran agreed to dismantle some of its nuclear program and open its facilities to more extensive international inspections.

Alongside the United States, France, Germany, the U.K., Russia and China ⁠were also signatories of the agreement.

In 2018, then-President Donald Trump kept a campaign promise and unilaterally withdrew the United States from the JCPOA calling it the "worst deal ever." Trump also reintroduced sanctions on Tehran that had been previously lifted.

Following Washington's exit from the landmark nuclear deal, other signatories of the pact ⁠have struggled to keep the agreement alive. 

The Biden administration is seeking a return to the deal and recently completed a sixth round of negotiations in Vienna.

On Thursday, a senior administration official told reporters on the condition of anonymity that the U.S. negotiating team had not reached a deal and would enter another round of talks but did not give further details on when the seventh round would begin.