Yemen’s Houthi rebels show no signs of ending their attacks on commercial ships in the Red Sea, the top commander of U.S. naval forces in the Middle East said Saturday.

Since the U.S. announced Operation Prosperity Guardian about 10 days ago, 1,200 merchant ships have traveled through the Red Sea region, and none has been hit by drone or missile strikes, Vice Admiral Brad Cooper said in an Associated Press interview.

He said additional countries are expected to sign on. Denmark was the latest, announcing Friday it plans to send a frigate to join the multinational security initiative that Defense Secretary Lloyd Austin announced on December 18 during a visit to Bahrain, where the Navy’s 5th Fleet is based, saying that “this is an international challenge that demands collective action.”

The narrow Bab el-Mandeb Strait connects the Gulf of Aden to the Red Sea and then the Suez Canal. The crucial trade route links markets in Asia and Europe. The seriousness of the attacks, several of which have damaged vessels, led multiple shipping companies to order their vessels to hold in place and not enter the strait until the security situation improved. Some major shippers were sending their ships around Africa and the Cape of Good Hope, adding time and costs to the journeys.

FILE - U.S. Navy Vice Admiral Brad Cooper speaks in Abu Dhabi, United Arab Emirates, Feb. 21, 2023. Since the U.S. announced Operation Prosperity Guardian, none of the 1,200 merchant ships that went through the Red Sea region was hit by drone or missile strikes, Cooper said.

FILE – U.S. Navy Vice Admiral Brad Cooper speaks in Abu Dhabi, United Arab Emirates, Feb. 21, 2023. Since the U.S. announced Operation Prosperity Guardian, none of the 1,200 merchant ships that went through the Red Sea region was hit by drone or missile strikes, Cooper said.

There are five warships from the United States, France, and the United Kingdom patrolling the waters of the southern Red Sea and the western Gulf of Aden, said Cooper, who heads the 5th Fleet. Since the operation started, the ships have shot down a total of 17 drones and four anti-ship ballistic missiles, he said.

Two days ago, the USS Mason, a Navy destroyer, shot down a drone and an anti-ship ballistic missile that were fired by the Iranian-backed Houthis, according to U.S. Central Command. The U.S. said the 22nd attack on international shipping by the Houthis since October 19 caused no damage to any of the 18 ships in the area or any reported injuries.

“I expect in the coming weeks we’re going to get additional countries,” Cooper said, noting Denmark’s recent announcement.

The U.S. has said that more than 20 nations are participating, but a number of those nations have not acknowledged it publicly.

Cooper said the coalition is in direct communication with commercial ships to provide guidance on “maneuvering and the best practices to avoid being attacked,” and working closely with the shipping industry to coordinate security.

An international task force was set up in April 2022 to improve maritime security in the region. But Cooper said Operation Prosperity Guardian has more ships and a persistent presence to assist vessels.

Since the operation started, the Houthis have stepped up their use of anti-ship ballistic missiles, Cooper said.

“We are clear-eyed that the Houthi reckless attacks will likely continue,” he said.

The Houthi rebels seized Yemen’s capital, Sanaa, in 2014, launching a grinding war against a Saudi-led coalition that sought to restore the government. The militants have sporadically targeted ships in the region, but the attacks increased since the start of the Israel-Hamas war.

The Houthis threatened to attack any vessel they believe is either going to or coming from Israel. That has escalated, with container ships and oil tankers flagged to countries such as Norway and Liberia being attacked or drawing missile fire.

The shipping company Maersk had announced earlier that it had decided to re-route its ships that have been paused for days outside the strait and Red Sea and send them around Africa instead. But on December 25, Maersk announced that it was going to resume sending ships through the strait, citing the operation. Cooper said another shipping company had also resumed using the route.

“Commerce is definitely flowing,” Cooper said.