SANAA/ADEN, Yemen - The death toll from US overnight airstrikes on Houthi sites across northern Yemen has risen to 31, with at least 101 others wounded, Al Jazeera reported Sunday.

The death toll is expected to rise further as US airstrikes continue across Yemen.

The casualties were reported across multiple locations, including the capital Sanaa, the northern province of Saada, a Houthi stronghold, as well as other Houthi-controlled Yemeni provinces.

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The military campaign, which started Saturday evening, struck the Al-Jarraf residential neighborhood in northern Sanaa, followed by several bombardments on the Shoab residential area in eastern Sanaa, Houthi-run al-Masirah TV reported.

Later in the evening, fresh strikes hit sites in the northern part of the province's namesake central city Saada, the group's northern main stronghold.

According to local residents, the strikes in Sanna targeted ammunition and rocket depots near the Houthi-controlled state television station in the Al-Jarraf neighborhood. A white smoke plume could be seen rising from the neighborhood, and a series of explosions were triggered following the airstrikes, witnesses said.

This is the first military operation conducted by the US military against the Houthi sites since US President Donald Trump assumed office in January and redesignated the group as a "foreign terrorist organization."

Trump posted on social media Truth Social that the aerial attacks on the "terrorists' bases, leaders, and missile defenses were to protect American shipping, air and naval assets, and to restore navigational freedom."

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He also warned the Houthis that if they do not stop their attacks "starting today ... hell will rain down upon you like nothing you have ever seen before."

In the meantime, the US Central Command posted footage on X showing warplanes taking off a US aircraft carrier in the Red Sea, saying that it "initiated a series of operations consisting of precision strikes against Houthi targets across Yemen to defend American interests, deter enemies, and restore freedom of navigation."

Following the US airstrikes, the Houthis vowed to launch retaliatory attacks, saying "this aggression will not pass without a response," and that the group is "fully prepared to confront escalation with escalation," the Houthis' political bureau said in a statement aired by al-Masirah TV.

On Tuesday, the Houthi group announced that it would resume launching attacks against any Israeli ship in the Red Sea, Arabian Sea, the Gulf of Aden and the Bab al-Mandab Strait until the Gaza Strip's crossings are reopened and aid allowed in.

From November 2023 to Jan 19, the Houthi group, which currently controls much of northern Yemen including the capital Sanaa, had launched dozens of drone and rocket attacks against Israel-linked ships and Israeli cities to show solidarity with Palestinians amid the ongoing Israel-Hamas conflict. The Houthis stopped their attacks on Jan. 19, when the Gaza ceasefire deal took effect.