A U.S. Navy destroyer was targeted on Wednesday in a failed missile attack from territory in Yemen controlled by Iran-aligned Houthi rebels, the second such incident in four days, the U.S. military said.

The USS Mason fired defensive salvos in response to at least one missile which did not hit the ship or caused any damage as it operated north of the Bab al-Mandab Strait, the Pentagon said. Indications are that the second salvo brought down an incoming missile, one U.S. official said, speaking on condition of anonymity.

The renewed attempt to target the U.S. Navy destroyer will add pressure on the U.S. military to retaliate, a move that would represent the first direct U.S. military action against Houthis in Yemen’s conflict. The Pentagon said it would respond “at the appropriate time and in the appropriate manner.”

The United States, a longtime ally of Saudi Arabia, has provided aerial refueling of jets from a Saudi-led coalition striking Yemen and it supplies U.S. weapons sales to the kingdom.

Michael Knights, an expert on Yemen’s conflict at the Washington Institute for Near East Policy, said the missile attacks appeared to be the Houthis’ response to an attack last weekend, widely blamed on Saudi-led forces, on mourners gathered in Yemen’s Houthi-held capital Sanaa.

The White House says it is reviewing its support for Saudi-led forces in Yemen in the wake of Saturday’s strike, which killed at least 140 people by one count.

Knights said the targeting of U.S. warship suggested the Houthis, fighters from a Shi’ite sect that ruled a 1,000-year kingdom in northern Yemen until 1962, could be becoming more militarily aligned with groups like Lebanon’s Shi’ite militant group Hezbollah.

“Targeting U.S. warships is a sign that the Houthis have decided to join the axis of resistance that currently includes Lebanese Hezbollah, Hamas and Iran,” Knight said.

The USS Mason was also the target of a failed missile attack off Yemen on Sunday, and the Navy praised the resolve of sailors aboard the ship.

“The team in USS Mason demonstrated initiative and toughness as they defended themselves and others against these unfounded attacks over the weekend and again today,” the Chief of Naval Operations Admiral John Richardson said.

“All Americans should be proud of them,” he said.

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