CHRISTIANSTED, U.S. Virgin Islands (AP) — Yemen’s Houthi rebels show no signs of ending their “ruthless” attacks on merchant ships in the Red Sea, the top commander of U.S. naval forces in the Middle East said Saturday, even as more nations join in join in. The international maritime mission to protect ships in vital water and commercial traffic is gaining momentum.

Since Operation Prosperity Guardian was announced just over 10 days ago, 1,200 merchant ships have sailed through the Red Sea region and none have been hit by drone or missile attacks, Vice Admiral Brad Cooper said in an interview with the Associated Press. He said it was expected that more countries would join. Most recently, Denmark announced on Friday that it plans to send a frigate to the mission, which Defense Secretary Lloyd Austin announced during a visit to Bahrain, where the Navy’s 5th Fleet is based, saying: “This is an international challenge , which requires collective action.”

The Iran-backed Houthis say their attacks are aimed at Israeli-linked ships to stop the Israeli offensive in Gaza.

The narrow Bab el-Mandeb Strait connects the Gulf of Aden with the Red Sea and then with the Suez Canal. The crucial trade route connects markets in Asia and Europe. The severity of the attacks, which damaged several ships, prompted several shipping companies to keep their ships in place and not enter the strait until the security situation improved. Some large shipping companies sent their ships around Africa and the Cape of Good Hope, making the trips more time-consuming and costly.

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

According to U.S. Central Command, the USS Mason, a Navy destroyer, shot down a drone and an anti-ship ballistic missile fired by the Houthis just two days ago. The U.S. said the Houthis’ 22nd attack on international ships since Oct. 19 did not cause any damage or reported injuries to any of the 18 vessels in the region.

“I expect we will add more countries in the coming weeks,” Cooper said, referring to Denmark’s recent announcement.

The U.S. has said more than 20 nations are participating, but some of those nations have not publicly acknowledged this.

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

In April 2022, an international task force was established to improve maritime security in the region. However, Cooper said Operation Prosperity Guardian has more ships and a sustained presence to help the ships.

Since the start of the operation, the Houthis have increased the use of anti-ship ballistic missiles, Cooper said. “We believe the Houthi’s ruthless attacks are likely to continue,” he said.

The Houthis seized Yemen’s capital, Sanaa, in 2014 and began a bitter war against a Saudi-led coalition seeking to restore the government. The militants have sporadically attacked ships in the area, but attacks have increased since the Israel-Hamas war began.

The Houthis have threatened to attack any ship they believe is traveling to or from Israel. That has seemingly spread to every ship, with container ships and oil tankers flying the flags of countries like Norway and Liberia being attacked or drawing rocket fire.

Shipping company Maersk had previously announced that it had decided to reroute its ships, which have been stranded outside the strait and the Red Sea for days, and sail around Africa instead. Maersk announced on December 25 that it would again send ships through the strait, citing the operation. Cooper said another shipping company also used the route again.

“The trade is definitely on,” Cooper said.

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Associated Press writer Lolita C. Baldor in Washington contributed to this report.