(Bloomberg) -- The US and its allies struck multiple targets in Houthi-controlled areas of Yemen on Saturday, responding to increased attacks on commercial shipping in the Red Sea region by the Iran-backed militant group.

The strikes on 18 Houthi sites at eight locations were the broadest announced since Feb. 3, providing new evidence that the Yemen-based militants are engaging the US and its allies in an extended battle. Targets included underground weapons storage sites, missile storage facilities, air defenses and one-way attack unmanned aerial systems, according to a Pentagon statement.

“The United States will not hesitate to take action, as needed, to defend lives and the free flow of commerce in one of the world’s most critical waterways,” US Defense Secretary Lloyd Austin said in a statement.

Despite repeated strikes by the US, the UK and their partners since mid-January, the Houthis have continued attacking naval and commercial vessels in the Red Sea, ostensibly as a means of pressuring Israel to end its war in Gaza against Hamas. The assaults have helped boost oil prices, with Brent pushing toward $84 a barrel last week, and upended trade through the southern Red Sea.

Read more: Iran-Backed Houthis Prepare for Long Red Sea Battle With US 

Sana’a, Yemen’s capital, was among the places targeted on Saturday, with residents reporting large explosions.

Pentagon spokeswoman Sabrina Singh said Thursday that Houthi attacks had increased over the previous 48 to 72 hours. US Central Command reported last week that US forces struck an unmanned underwater vessel, or underwater drone, in the first sighting of such a device since Houthi attacks began in October.

Supporting the strikes on Saturday were Australia, Bahrain, Canada, Denmark, the Netherlands and New Zealand.

“Our aim remains to de-escalate tensions and restore stability in the Red Sea, but we will once again reiterate our warning to Houthi leadership: we will not hesitate to continue to defend lives and the free flow of commerce in the face of continued threats,” the countries said in the Pentagon statement. 

--With assistance from Mohammed Hatem.

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