The U.S.-led coalition in Iraq and Syria conducted airstrikes against forces loyal to the regime of Syrian President Bashar al-Assad near At Tanf, a restive area on the country’s southern border with Iraq and Jordan, on May 18, defense officials told multiplemedia outlets.

A Pentagon official said U.S. military jets targeted a pro-regime Shia militia armed and equipped by the Assad government and “deemed a threat to U.S. partners near Jordan,” Stars and Stripes reports.

The airstrikes were characterized to reporters as a “defensive,” targeting militia fighters “advancing well inside an established de-confliction zone,” northwest of the At Tanf, CENTCOM said in a statement.

The bombing was carried out “after apparent Russian attempts to dissuade Syrian pro-regime movement south towards At Tanf were unsuccessful, a coalition aircraft show of force, and the firing of warning shots,” according to CENTCOM.

A DoD official told Voice of America that the strikes were “not a change in policy but instance of commander on the ground's decision for force protection.”

BuzzFeed, which first reported the airstrikes, has additional details:

Unlike the US strike against the al-Shayrat air base in March, which the Trump administration ordered in retaliation for a regime chemical weapons attack, Thursday’s strike seemed designed to protect the US forces based at Tanf.

One of the defense officials — who, like the others, spoke on condition of anonymity to reveal details that the Pentagon had yet to make public — said that the US acted to stop an advance of pro-regime forces toward Tanf. Pro-regime forces had crossed a pre-agreed deconfliction zone and continued to advance despite warning strikes, he added.

CENTCOM told the media that the strike destroyed “construction equipment and a tank.”

The reported bombing came just days after the Treasury Department announced a new round of sanctions against Syrian companies and individuals on May 16, citing the Assad regime’s “relentless attacks on civilians.”

The day before Treasury announced the new sanctions, a State Department spokesman presented evidence that the Assad regime had killed thousands of prisoners and constructed a crematorium outside the notorious Sednaya military prison, north of Damascus, to “dispose of detainees' remains with little evidence.”

A State Department spokeswoman said on May 17 that the U.S. would continue to pressure the Russian government to drop its support of the Assad regime. In April, National Security Advisor H.R. McMaster declared that Moscow’s continued support for Assad and other regional forces “clearly cut against Russian interest.”

The airstrikes came just over a month after the U.S. military launched about 60 Tomahawk cruise missiles from the USS Ross and USS Porter at the al-Shayrat military air base southeast of Homs, in response to a gas attack against Syrian civilians by pro-regime forces in early May.