The United Kingdom, Bahrain, Canada, France, Italy, Netherlands, Norway, Seychelles and Spain will join the U.S. in the new mission, Austin announced. Some of the countries will conduct joint patrols while others provide intelligence support in the southern Red Sea and the Gulf of Aden.

Several other countries have also agreed to be involved in the operation but prefer not to be publicly named, a defense official said on the condition of anonymity to discuss additional details of the new mission that have not been publicly announced.

The mission will be coordinated by the already existing Combined Task Force 153, which was set up in April 2022 to improve maritime security in the Red Sea, Bab el-Mandeb and the Gulf of Aden. There have been 39 member nations in CTF 153, but officials were working to determine which of them would participate in this latest effort.

Separately, the United States has also called on the United Nations Security Council to take action against the attacks.

In a letter to council members obtained Monday by The Associated Press, U.S. Ambassador Linda Thomas-Greenfield said Houthi attacks targeting commercial vessels legally transiting the international waterways continue to threaten “navigational rights and freedoms, international maritime security, and international commerce.”

The 15 council members discussed the Houthi threat behind closed doors Monday but took no immediate action.

Three U.S. warships — the USS Carney and the USS Mason, Navy destroyers — have been moving through the Bab el-Mandeb Strait daily to help deter and respond to attacks from the Houthis.

The move to set up the expanded operation came after three commercial vessels were struck by missiles fired by Iranian-back Houthis in Yemen on Dec. 3. Those attacks were part of an escalating campaign of violence that also included armed and other drones launched in the direction of U.S. warships.

To date the U.S. has not struck back at the Iranian-back Houthis operating in Yemen or targeted any of the militants’ weapons or other sites. On Monday Austin did not answer a question as to why the Pentagon had not conducted a counterstrike.