U.S. forces in eastern Syria came under rocket fire, with no reported casualties, in an escalation a day after the Pentagon said U.S. air strikes targeted facilities on the Iraq-Syria border used by Iran-aligned militias to attack U.S. interests in Iraq.
U.S. troops "were attacked by multiple rockets" in eastern Syria on June 28, but there were no casualties and soldiers responded with “counter-battery artillery fire at rocket launching positions,” said coalition spokesman Wayne Marotto on Twitter.
According to the Syrian Observatory for Human Rights, a Britain-based war monitor, pro-Iranian militias fired several shells at a U.S. base in the Al-Omar oil field in eastern Syria, where U.S. forces back the Kurdish-led Syrian Democratic Forces fighting the Islamic State extremist group.
The Pentagon announced on June 27 that U.S. President Joe Biden ordered "defensive" air strikes on operational and weapons storage facilities used by militias at two locations in Syria and one location in Iraq.
It said the facilities near the border were used by Iran-backed militia groups, including Kata'ib Hizballah and Kata'ib Sayyid al-Shuhada, to stage drone attacks against U.S. interests in Iraq.
During a visit to Rome on June 28, U.S. Secretary of State Antony Blinken said the United States took “necessary, appropriate action” when it launched the air strikes, and said they were “designed to limit the risk of escalation, but also to send a clear and unambiguous deterrent message.”
Iraq’s government called the U.S. air raid a violation of the country’s sovereignty and said it would "study all legal options" to prevent such action being repeated. Syria described it as a "flagrant violation of the sanctity of Syrian and Iraqi lands."
Iraqi militia groups issued a statement saying four members of the Kata'ib Sayyid al-Shuhada faction were killed in the strikes and vowed to retaliate. The groups said the militiamen were stationed there to prevent Islamic State fighters from infiltrating Iraq.
U.S. and Israeli officials have previously said the militia groups help Iran operate a land corridor to funnel weapons and supplies to Syria and onward to Lebanon.
The U.S. air strikes came after Iraqi Kurdish officials said on June 26 that four explosive-laden drones hit locations outside the semiautonomous region's capital, Irbil. No casualties were reported.
The same day, the Popular Mobilization Forces (PMF), or Hashed al-Shaabi, a paramilitary alliance opposed to the U.S. presence in Iraq, held a military parade near Baghdad attended by senior officials, including Prime Minister Mustafa al-Kadhimi.
The PMF is a state-sanctioned umbrella organization of mostly Shiite militias backed by Iran that was originally formed in 2014 to fight the Islamic State extremist group.
Critics say the militias have established a parallel power structure with allies in parliament and government, including in the security field.
The air strikes on June 27 were the second in the region ordered by Biden since he took office six months ago.
In February, the U.S. military launched air strikes against facilities used by the same Iran-backed militia groups on the Iraq-Syria border.
Those air strikes were in response to what the U.S. military said at the time were rocket attacks that killed one civilian contractor and wounded a U.S. service member and other coalition troops.
The United States blames Iran-backed militias for repeated rocket attacks on the U.S. Embassy in Baghdad and at Iraqi bases housing some 2,500 U.S. troops as part of an international mission against the Islamic State group.
In April, an explosive-laden drone hit the coalition's Iraq headquarters in the military section of Irbil airport.
General Kenneth Mckenzie, the top commander of U.S. forces in the Middle East, has identified small drones as a major concern in the region because they can more easily evade air defenses.
Under former U.S. President Donald Trump, tensions between Washington and Tehran escalated in January 2020 when a U.S. drone strike in Baghdad killed Iran’s top general, Qasem Soleimani, and Abu Mahdi al-Muhandis, the leader of Kata'ib Hizballah and deputy chief of the PMF.
The death of the two commanders led to growing calls from Iraqi militia groups and allied political parties to expel U.S. forces from Iraq.
A rocket attack blamed on Kata'ib Hizballah in December 2019 killed a U.S. defense contractor and wounded several U.S. and Iraqi soldiers at a military base in the northern Iraqi city of Kirkuk, touching off a cycle of escalation that led to Soleimani's killing and Iran launching retaliatory ballistic missiles at Iraqi bases housing U.S. troops.