The Houthis are increasingly operating independently of Tehran, posing a "clear and very present danger" on the international stage as the terror group rearms and sharpens its strike capabilities, a former U.S. envoy warned Thursday.

The warning came amid deadly missile and drone attacks on Saudi Arabia in recent days and growing threats to global shipping routes and critical Middle East infrastructure in the run-up. 

Turki al-Maliki, spokesperson for the Saudi-led coalition in Yemen, also confirmed Thursday that Houthi attacks on King Khalid International Airport in Riyadh had killed 17 and injured 333 others from Oct. 7-11.

Speaking at a news conference in Riyadh, al-Maliki said the Oct. 10 attack involved 10 drones, missiles and other projectiles. 

"King Khalid International Airport has been subjected to 20 attacks since (Oct. 1)," he noted.

"The Saudis were very clear to our leaders that they viewed the Houthis as a major threat," Lenderking said of his time in the kingdom a decade ago.

At the time, he said, the group was "quietly building up their capability, burnishing their narrative of why they sought to lead Yemen as a messianic group, as a group from northern Yemen, with an agenda, with a mission."

The Houthis had emerged as a religious and political movement in Yemen in the 1990s, but their ties to Iran developed into a military partnership after 2014, when Tehran expanded its assistance and training during Yemen's civil war.

"The Houthis don't really need the Iranians anymore," Lenderking, a former acting assistant secretary for Near Eastern affairs at the U.S. State Department, continued, adding it was still "a very important relationship that "enabled the Houthis to become the powerful force that they are."

Lenderking, now a distinguished diplomatic fellow at the Middle East Institute (MEI), said, over time, the Houthis had developed their own "homegrown indigenous capability" as they capitalized on any disunity across the Gulf region.

Saturday's missile and drone attack on King Khalid International Airport in Riyadh raised concerns that President Donald Trump could be drawn into a broader regional conflict as Saudi Arabia seeks U.S. assistance. 

Asked whether the U.S. would defend Saudi Arabia against further attacks, Trump said, "You'll find out soon."

Speaking at an MEI briefing, Lenderking said the Houthis' sophisticated weapons and targeting capabilities have transformed the group from a regional insurgency into an international security threat.

"They have the capability to hit around the region, including up into the northern reaches of the Red Sea. So, this is a regional problem, and given the fact that the Houthis control the west coast of Yemen," Lenderking said.

"It's an international problem now." 

Lenderking cited the precision of the Riyadh airport attack as evidence of the Houthis' growing capabilities compared with earlier strikes during the Gaza conflict.

"They can hit things better. Now, they are hitting Terminal Four of Riyadh Airport, very specifically. It's a clear and very present danger," he said.

The Houthis reportedly launched multiple drones followed by cruise and ballistic missiles that traveled more than 620 miles to Riyadh, prompting an investigation into possible Saudi air defense failures, according to The Associated Press, citing regional officials.

Saudi forces intercepted two more ballistic missiles targeting Riyadh on Monday. On Tuesday, a Houthi strike caused damage to Aramco's headquarters in Dhahran, sparking a fire that spread across several floors, black-market oil sales, taxation and extortion while also forcing families to provide recruits, allowing the group to continue fighting even if Iranian assistance is cut off.

"They have had support from Iran over the years, so they have money in the bank from that," Lenderking said. 

"They relied on sales of black market oil in the past. They extort Yemeni transport companies, businesses. They tax people in areas that they control. They force many families to offer up a son to fight on the front lines."

The Houthis' expanding arsenal has raised concerns about potential Chinese involvement in their weapons supply networks.

Yemen's government has accused the rebels of seeking Chinese components for medium-range ballistic missiles, raising concerns about the group's access to advanced military technology.

"There is a Chinese connection here that's very detrimental," Lenderking warned, adding that front companies have helped the group obtain weapons through commercial channels.

Lenderking warned that the Houthis could also target Saudi energy facilities, pipelines and desalination plants, infrastructure critical to the kingdom's economy and water supply. 

"The Houthis have hit pipelines," he said. "They have diesel plants and other energy infrastructure in their sights."

Attacks on such facilities could disrupt global energy markets, maritime commerce and regional stability.

The Houthis also control Yemen's western coastline along the Red Sea, a vital shipping corridor connecting Europe and Asia.

With the rebels now capable of striking targets hundreds of miles away, Lenderking warned that the threat extends far beyond Yemen's borders.

"One blast at Riyadh Airport is a huge statement," the expert said.

"That's why I come back to the fact that this is an international conflict," he said, adding that "immediate action is required."