A cargo ship that was struck by a Houthi ballistic missile on Monday has created an 18-mile long oil slick in the Red Sea as it continues to take on water, two US officials said Friday.

The M/V Rubymar — a Belize-flagged, UK-registered, Lebanese-owned vessel — was carrying 41,000 tons of fertilizer when it was struck on Monday by one of two ballistic missiles fired from Houthi territory in Yemen.

The U.S. launched five "self-defense" airstrikes against a series of Houthi rebel positions in Yemen on Saturday.

The strikes targeted three anti-ship missile batteries, one unmanned underwater vessel (UUV) and another unmanned surface vessel (USV), U.S. Central Command (CENTCOM) announced Sunday.

"This is the first observed Houthi employment of a UUV since attacks began in Oct. 23," CENTCOM said in a statement.

American forces hit an undersea drone during five "self-defense strikes" against Houthi rebels in areas of Yemen controlled by the Iran-backed rebels, U.S. Central Command said Sunday.

Why it matters: This is the first time U.S. forces have observed Houthis using an unmanned underwater vessel (UUV) since the group began attacking merchant and commercial ships passing through the Red Sea on Oct. 23, per a CENTCOM statement on Saturday's strikes.

The United States conducted five self-defense strikes in areas of Yemen controlled by the Iranian-backed Houthi militia, U.S. Central Command said on Sunday.

It said it struck three mobile anti-ship cruise missiles, one unmanned underwater vessel and one unmanned surface vessel on Saturday.

"This is the first observed Houthi employment of a UUV since attacks began in Oct. 23," CENTCOM said in a post on X.

After the United States and United Kingdom's new wave of strikes in Yemen, the Houthis vowed a response. The US-UK airstrikes "will not deter us", said Houthis after the strikes hit dozens of Iran-backed rebels' targets over the Red Sea attacks.

The Yemen airstrike comes after the US retaliatory strikes targeting Iran-backed stations in Iraq in Syria. The retaliatory strikes on Friday was a response to the drone attack in Jordan by militias in Iran, that killed 3 US soldiers.

The US carried out further strikes against the Iran-backed Houthi group in Yemen early on Sunday, the US military said.

Centcom said the US struck a land-attack cruise missile and four anti-ship missiles that "were prepared to launch against ships in the Red Sea".

The additional strikes came a day after joint US-UK strikes on Houthi targets.

The US has also warned that it intends to take further action against Iran-backed groups in Iraq and Syria.

Houthi rebels vowed "escalation" in reaction to U.S. and U.K. strikes launched in Yemen on Sunday.

A spokesman for the Iran-backed group vowed to continue its campaign of disrupting regional trade "no matter the sacrifices it costs us." The U.S. and U.K. launched a series of attacks on Houthi targets in Yemen this weekend in reaction to a lethal drone attack on a U.S. base in Jordan last week.

The U.S. Central Command (CENTCOM) announced that its forces conducted a self-defense strike against Houthi forces early Sunday morning.

In a statement published on X Sunday evening, CENTCOM explained that American forces "struck four anti-ship cruise missiles, all of which were prepared to launch against ships in the Red Sea."

"U.S. forces identified the missiles in Houthi-controlled areas of Yemen and determined they presented an imminent threat to U.S. Navy ships and merchant vessels in the region," CENTCOM's statement read.

U.S. and U.K. forces combined to hit 36 Iran-backed Houthi rebel targets across 13 locations in Yemen on Saturday, marking the third joint mission between the two Western allies in the Middle Eastern nation.

U.S. Secretary of Defense Lloyd Austin said the strikes were intended to degrade the Houthis’ capabilities to carry out attacks against commercial vessels in the frequently navigated waterways off Yemen’s coast.

Tehran was not involved in the drone attack on a US base in Jordan which left three service members dead and more than 30 wounded, Iranian Foreign Ministry spokesman Nasser Kanaani said on Monday. 

The Islamic Resistance in Iraq – an umbrella group for Islamist Shia militias – claimed responsibility for the strike on the outpost known as Tower 22, not far from the border with Jordanian-Syrian border.