The US air force bombed nine targets in Syria, Centcom said on Tuesday, claiming the strikes were in response to attacks by Iran-backed militias against its forces.

The strikes, carried out over a 24-hour period, represent the latest in years of clashes in eastern Syria in the aftermath of the international struggle against ISIS. That conflict has left about 900 US soldiers present, assisting Kurdish militia groups who worked with them, with the coalition in loose control of swathes of the country’s east bordering Iraq.

The fresh clashes between US forces and groups largely equipped and funded by Iran comes amid reports that the incoming Donald Trump administration has tapped Iran-hawks for top cabinet positions. Trump has, however, has long said he wishes to withdraw US forces from Syria.

The US also conducts air strikes against ISIS on a near-monthly basis, amid continuing reports that the group is attempting to regenerate in Syria. Centcom’s statement said its forces were present to “defeat ISIS”, and that the militia attacks could disrupt the effort.

Israel too, has conducted almost-weekly strikes in Syria, mainly against Iran-linked targets in what it says are attempts to cut off weapons supplies to Lebanon's Hezbollah, but also hitting government forces, and civilians.

Iran-backed groups have also sporadically attacked US forces co-located with the Iraqi army in western Iraq’s Anbar desert province.

According to the Washington Institute for Near East Policy, a think tank which has been tracking attacks by the militias, the groups have launched nearly 200 attacks on US forces since the October 7 Israel-Gaza war began, aligning themselves with Hamas and Iran’s wider regional militia alliance, which includes Yemen’s Houthis and Lebanon’s Hezbollah.

In Iraq, through a coalition called the Islamic Resistance, which includes powerful Iran-armed groups such as Kataib Hezbollah, they have threatened more attacks if Israel launches another retaliation on Iran, following waves of tit-for-tat ballistic missile and air strike campaigns by the two rivals, since April.

A recent Washington Institute report said many militia attacks against US forces amounted to intimidation and “aimed to miss” but would probably “draw a lethal US response”, eventually.

No US personnel were injured in the recent militia attacks, but as of late Monday the Pentagon did not provide further details on what US sites in Syria had been attacked or which sites the US struck in return.

Nonetheless, the simmering conflict has the potential to rapidly escalate. In February the US launched a massive attack that included 85 air strikes on Iranian-backed militia sites in Syria and Iraq, in response to a drone attack in Jordan that killed three US soldiers.

Syria and Iraq could remain a significant flashpoint between the US and Iran next year, amid reports that Donald Trump could nominate Marco Rubio for Secretary of State and Mike Waltz for National Security Advisor. Both take a hard line on Iran, urging a tougher US response to its nuclear research program and network of regional militias.