• U. S. military drone shot down over northern Yemen,

CAIRO — An American military drone was shot down in a rugged patch of northern Yemen, said U. S. officials and Yemeni rebels, immediately triggering accusations of Iranian involvement in a region where tensions between Washington and Tehran are growing.

On Wednesday, a military spokesman for the Iran- aligned rebels, known as the Houthis, said in a tweet and on the group’s television station, al- Masirah, that an MQ- 9 reaper drone was brought down by the rebels’ air defense system late Tuesday.

Lt. Col. Earl Brown, a spokesman for U. S. Central Command, said in a statement, “We are investigating reports of an attack by Iranian- backed Houthis ... on a U. S. unmanned aircraft system ( UAS) operating in authorized airspace over Yemen.”

U. S. officials, speaking on the condition of anonymity to discuss undisclosed details of the event, said an American MQ- 9 drone had been shot down.

The attack, the second such incident in three months, threatens to worsen tensions in a region that has become a battleground for the United States and its Sunni Muslim allies against Shiite Iran. On Wednesday, Col. Brown said, “We have been clear that Iran’s provocative actions and support to militant and proxies, like the Iranian- backed Houthis, poses a serious threat to stability in the region and our partners.”

In June, the U. S. military said the Houthis had shot down a U. S. drone with Iranian assistance. The attacks underscore the growing military capabilities of the rebels, who only a few years ago were mountain fighters with no access to armed drones or the surface- to- air missiles that they claimed were used to strike the U. S. drones.

Houthi military spokesman Yahya Saria claimed in a tweet that the missile that brought down the MQ9 drone was “built locally and will be unveiled soon at a press conference.”

“We affirm to the powers of aggression that they need to think about the consequences of their actions,” Mr. Saria said. “Our aerial zone will no longer be violated like before.”

It was unclear what mission the U. S. military drone was undertaking, but the U. S. military has deployed drones and airstrikes in previous years to target Yemen’s al- Qaida affiliate, known as al- Qaida in the Arabian Peninsula.

The United States is backing a Saudi- led coalition of regional Sunni countries that is fighting the Shiite Houthis to help restore Yemen’s internationally recognized government and stem Iran’s regional influence. Iran has denied providing military and financial backing to the Houthis.

Tensions between the United States and Iran have escalated since the Trump administration withdrew from an international pact to contain Iran’s nuclear capabilities and increased sanctions.