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.

Treasury says 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.

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.

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Associated Press reporter Lolita Baldor contributed to this report.