WATCH: White House holds briefing as the U.S. sanctions money lending network to Yemen’s Houthi rebels

WASHINGTON (AP) — Responding to increased attacks on ships in the southern Red Sea by Iranian-backed Houthi rebels, the U.S. announced sanctions against 13 people and firms alleged to be providing tens of millions of dollars from the sale and shipment of Iranian commodities to the Houthis in Yemen.

Watch the briefing in the player above.

The White House also announced Thursday that it was encouraging allies to join the Combined Maritime Forces, a 39-member partnership that exists to counter malign action by non-state actors in international waters, as it looks to push back against the Houthis. The State Department and Pentagon are leading the effort to expand the maritime partnership after three commercial vessels were struck by missiles fired by Iranian-back Houthis in Yemen earlier this week.

The strike marked an escalation in a series of maritime attacks in the Mideast linked to the Israel-Hamas war, as multiple vessels have found themselves in the crosshairs of a single Houthi assault for the first time in the conflict. The U.S. vowed to “consider all appropriate responses” in the wake of the attack, specifically calling out Iran, which is the chief sponsor of both Hamas militants in Gaza and the Houthis in Yemen.

In the new sanctions announced Thursday, Treasury said that previously sanctioned Houthi and Iranian financial facilitator Sa’id al-Jamal uses a network of exchange houses and firms to help Iranian money reach the country’s militant partners in Yemen.

The sanctions block access to U.S. property and bank accounts and prevent the targeted people and companies from doing business with Americans.

Money lenders in Lebanon, Turkey and Dubai are listed for assisting al-Jamal, along with shipping firms from Russia to St. Kitts and Nevis, which allegedly move al-Jamal’s Iranian commodity shipments. All people and firms were hit with sanctions Thursday.

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Brian Nelson, Treasury’s under secretary for terrorism and financial intelligence, said the Houthis “continue to receive funding and support from Iran, and the result is unsurprising: unprovoked attacks on civilian infrastructure and commercial shipping, disrupting maritime security and threatening international commercial trade.”

“Treasury will continue to disrupt the financial facilitation and procurement networks that enable these destabilizing activities.”

Since October, the Houthis have launched missile and drone attacks over commercial shipping operations in the Red Sea and the Gulf of Aden.

The Houthis have sporadically targeted ships in the region over time, but the attacks have increased since the start of the war between Israel and Hamas, spiking after an Oct. 17 explosion at a hospital in Gaza killed and injured many. Houthi leaders have insisted Israel is their target.

White House National Security Council spokesman John Kirby said that the U.S. has already heard from “several key partners” interested in potentially joining the Combined Maritime Forces.

The maritime partnership focuses on counter-narcotics, counter-smuggling, suppressing piracy and promoting a safe maritime environment. When requested, CMF assets at sea respond to environmental and humanitarian incidents.

“Our focus at this time is ensuring that there are sufficient military assets in place to deter these Houthi threats to maritime trade in the Red Sea and in the surrounding waters to the global economy writ large,” Kirby said.

The White House announced earlier this week that the U.S. may establish a naval task force to escort commercial ships in the Red Sea. National security adviser Jake Sullivan said on Monday that the U.S. has been in active conversations with allies about setting up the escorts, though nothing was finalized.

Kirby stressed that the U.S. is “not in an armed conflict with the Houthis per se” but is determined to protect and determine freedom of navigation.

“This is an international problem. And it demands an international solution and that is exactly the approach that the United States is going to take to it now,” Kirby said.

Associated Press writers Lolita C. Baldor and Aamer Madhani contributed to this report.