The US conducted a new round of airstrikes against facilities used by Iran and its proxies in eastern Syria late Sunday in retaliation for a spate of recent attacks against US troops, Pentagon officials said Sunday.

Officials said the strikes most likely killed or injured an undetermined number of people at the sites.

The airstrikes appeared to mark an escalation by the Biden administration, which had previously conducted two sets of airstrikes that officials said were meant to deter Iran’s Islamic Revolutionary Guard and the militias it supports in Syria and Iraq. US officials had said those strikes had caused no known casualties.

On Sunday night, Air Force F-15E fighter jets struck several buildings in Abu Kamal used for training, logistics and storing munitions, as well as a safe house in Mayadin used as a command headquarters, the officials said. The strikes came just four days after American warplanes hit a munitions warehouse in eastern Syria. An earlier set of US retaliatory strikes came on October 27.

US officials blame Iran and the militias aligned with it for what has become a daily barrage of rocket and drone attacks against US forces in Iraq and Syria.

But President Joe Biden had in recent weeks rejected more aggressive bombing options proposed by the Pentagon out of fear of provoking a wider conflict with Iran.

Pentagon and other Biden administration officials rejected that criticism Sunday, saying that the latest American airstrikes were intended to disrupt the militias’ activities and to put their personnel at risk, not just their munitions or buildings.

“The President has no higher priority than the safety of US personnel, and he directed today’s action to make clear that the US will defend itself, its personnel and its interests,” defence secretary Lloyd Austin said in a statement while travelling in Asia.

Pentagon officials said that fewer than a dozen Iran-backed militia personnel were present at the bombed sites Sunday and that it was likely some were killed or injured in the attack. However, American analysts were unable to provide a more precise casualty estimate.

The Pentagon said on Sunday that there had been at least 48 attacks against US forces in Syria and Iraq since October 17 and that at least 56 US service members had been injured. Roughly half of those suffered traumatic brain injuries, and two had to be flown to Landstuhl military hospital in Germany for treatment.

The US has 2,500 troops in Iraq and 900 in Syria, mostly to help local forces fight remnants of the Islamic State group. The US has been shifting military assets to West Asia since Hamas’ surprise attack against Israel on October 7 to try to prevent a regional war that could drag American forces into conflict with Iranian proxies in Lebanon, Yemen, Iraq and Syria.

It has deployed one aircraft carrier to the eastern Mediterranean near Israel, and another recently left the Red Sea and is sailing to the Arabian Sea. The Pentagon has also sent additional warplanes to the Persian Gulf region, as well as Patriot anti-missile batteries and other air defences to several Gulf nations.

New York Times News Service