Last week's attack on the UAE vessel also took place around the Bab al-Mandab strait, in what the UAE branded an "act of terrorism."

In 2013, more than 3.4 million barrels of oil passed through the 20 km (12 mile)-wide Bab al-Mandab each day, the US Energy Information Administration says.

It was unclear what actions the US military might take, but Davis stressed a commitment to defend freedom of navigation and protect US forces.

"We will continue to take all necessary steps to ensure the safety of our ships and our servicemembers," he said.

The attack also came the same day that Yemen's powerful former president, Ali Abdullah Saleh, a key Houthi ally, called for an escalation of attacks against Saudi Arabia, demanding "battle readiness at the fronts on the (Saudi) border".

An estimated 10,000 people have been killed in Yemen's war. The United Nations blames Saudi-led coalition strikes for 60 percent of some 3,800 civilian deaths since they began in March 2015.