A series of attacks on Saudi airports through Sunday reportedly killed at least 14 people, including an American, and injured more than 300, according to the source. Saudi Arabia’s civil aviation authority said a separate Sunday strike killed a Pakistani resident and wounded 11 others. An airport in Dammam was also reportedly targeted.

The Houthis claimed responsibility for earlier attacks on King Khalid International Airport in Riyadh. U.S. officials blamed the group for a Saturday strike that reportedly killed 13 people and injured more than 300. The Houthis renewed warnings Sunday, urging airlines, airport workers and travelers to stay away from Saudi airports. Saudi Arabia said it would retaliate.

Secretary of State Marco Rubio condemned Saturday’s attack and confirmed an American was among those killed. President Donald Trump said the United States might become involved in Saudi Arabia’s military campaign against the Houthis, but left the decision open.

Behnam Ben Taleblu, an Iran specialist at the Foundation for Defense of Democracies, described the attacks as part of a broader pattern of escalation and connected the focus on aviation to U.S. restrictions on Iran’s aviation sector. He also pointed to a Sept. 23 warning by Iranian official Mohsen Rezaei about neighboring countries’ airports if they assisted U.S. efforts to restrict Iranian flights.

Iran has long supported the Houthis, but the extent of Tehran’s involvement in these attacks has not been independently established. The source also notes reports of Russian intelligence and technical assistance to the Houthis, while describing some related allegations as unproven.