An unprecedented wave of rocket and drone attacks targeted US diplomats and troops in Iraq and Syria since early Wednesday local time, including at least 14 rockets hitting an Iraqi air base hosting US forces, wounding two American service members.

Iraqi army officials said the pace of recent attacks against bases hosting U.S. forces with rockets and explosive-laden drones was unprecedented.

While there were no immediate claims of responsibility for the attacks - part of a wave targeting US troops or areas where they are based in Iraq and Syria - analysts believed they were part of a campaign by Iranian-backed militias.

Iraqi militia groups aligned with Iran vowed to retaliate after US strikes on the Iraqi-Syrian border killed four of their members last month.

Two rockets were fired at the US Embassy inside Baghdad's Green Zone early on Thursday, Iraqi security sources told Reuters.

The embassy's anti-rocket system diverted one of the rockets, said one of the sources - a security official whose office is inside the Green Zone. The second rocket fell near the zone's perimeter, security officials said.

Sirens blared from the embassy compound inside the zone, which houses government buildings and foreign missions, the sources said.

The Pentagon said a drone had been brought down in eastern Syria and that no US service members had been injured and there had not been any damage.

On Tuesday, a drone attacked Erbil airport in northern Iraq, targeting a US base on the airport grounds, Kurdish security sources said. Three rockets also landed on Ain al-Asad on Monday without causing casualties.

ESCALATION

The United States has been holding indirect talks with Iran aimed at bringing both nations back into compliance with the 2015 Iran nuclear deal, which was abandoned by then-President Donald Trump. No date has been set for a next round of the talks, which adjourned on June 20.

Hamdi Malik, an associate fellow at the Washington Institute and a specialist on Iraq’s Shi’ite militias, said the attacks were part of a coordinated escalation by Iranian-backed militias in Iraq.

The attempt to strike in eastern Syria appeared to be the first example of operations being carried out simultaneously in both countries.

"It seems to me they have the green light from Iran to escalate, especially given that the nuclear negotiations are not going well. But at the same time, they do not want to escalate beyond a certain point – they are more vulnerable to US air strikes than they used to be - and they don’t want to overcomplicate the negotiations Iran is holding with the West."

The United States told the UN Security Council last week that it targeted Iranian-backed militia in Syria and Iraq with air strikes to deter them and Tehran from conducting or supporting further attacks on US personnel or facilities.

Iran denied supporting attacks on US forces in Iraq and Syria and condemned US air strikes on Iranian-backed groups. But militia groups who depend on Iran for training, weapons and finances would hardly escalate attacks without at least Tehran’s tacit agreement.

Reporting by Reuters