Iranian-backed Shiite Houthi rebels reportedly shot down a U.S. drone flying over Yemen on Tuesday, marking the second such incident since June.

U.S. Central Command (CENTCOM) — charged with American military activity in and around the Middle East — acknowledged the most recent incident in a statement issued Wednesday.

U.S. Army Lt. Col. Earl Brown, a spokesman for CENTCOM, said:

We are investigating reports of an attack by Iranian-backed Houthis forces on a U.S. unmanned aerial system (UAS) operating in authorized airspace over Yemen.

We have been clear that Iran’s provocative actions and support to militants and proxies, like the Iranian-backed Houthis, poses a serious threat to stability in the region and our partners.

Citing two U.S. officials who spoke on condition of anonymity, Reuters reports that the MQ-9 drone went down in Yemen’s Dhamar province, located southeast of the Houthi-controlled capital of Sanaa.

Reuters adds:

This is not the first time a U.S. drone has been shot down in Yemen. In June, the U.S. military said that Houthi rebels had shot down a U.S. government-operated drone with assistance from Iran.

…

[One of the U.S. officials] said that while losing a drone was expensive, it was not unprecedented and it was unlikely to lead to any major response by the United States.

Echoing one of the anonymous U.S. officials, a spokesman for the Houthis reportedly claimed responsibility for bringing down the U.S. drone on Tuesday.

One of the American officials indicated the Iran-aligned Houthi rebels shot down the unmanned aerial vehicle (UAV) with a surface-to-air missile.

“It appears to have been fired by the Houthis and enabled by Iran,” the official said, without elaborating further.

The other U.S. official cautioned that it was too early to say what brought the drone down.

Via Twitter, Houthi military spokesman Yahya Sari said the Shiite group used a rocket allegedly “developed locally” to shoot down the aircraft, Reuters points out.

The U.S. has repeatedly accused Iran of providing missiles and other military support to the Houthis, an allegation denied by Tehran.

Earlier this month, however, Iran’s supreme leader, Ayatollah Ali Khamenei, vowed to continue supporting the Houthis against the Saudi-led coalition.

The U.S. occasionally launches drone attacks and airstrikes against members of the Yemen-based al-Qaeda in the Arabian Peninsula (AQAP).

AQAP has capitalized on the U.S.-backed Saudi coalition’s primary focus on defeating Houthis to strengthen its influence and territorial control. The U.S. has also targeted the Islamic State (ISIS/ISIL), an AQAP rival, in Yemen.

Moreover, the U.S. provides support to the Saudi coalition in the form of intelligence, logistical assistance, and military advice.

Since March 2015, the Saudi-led Sunni alliance has been fighting to restore the internationally-recognized government of President Abd-Rabbu Mansour Hadi, to no avail.

In late 2014, the Houthis conquered the Yemeni capital of Sanaa, pushing the Hadi government out.

Iran-allied Houthis have targeted U.S. Navy ships with missiles. They also regularly fire rockets across the Yemen border into Saudi Arabia.

Regional foes Sunni Saudi Arabia and Shiite Iran have been fighting a proxy war for more than four years.

The conflict has devastated Yemen and triggered what analysts describe as the worst humanitarian crisis in the world, bringing Yemen to the brink of famine.

Several estimates show that the Yemen war has killed more than 90,000 people, including many children.

U.S. President Donald Trump vetoed a bill that called for an end to America’s support for Saudi Arabia in Yemen.

U.S. support for the Saudi-led alliance has “inadvertently” aided al-Qaeda, an expert from the conservative American Enterprise Institute (AEI) acknowledged in March, echoing other assessments.

The American drones went down in Yemen amid heightened tensions between the United States and Iran.

President Trump’s “maximum pressure” campaign currently choking the Iranian economy has strained the relationship between the two countries, bringing them closer to a military conflict.

The Trump administration reimposed sanctions suspended under the controversial Iran nuclear deal as part of an unprecedented wave of crippling economic restrictions. President Trump pulled the U.S. of the nuclear pact, arguing that it was not tough enough on Iran.