Houthis have stepped up their hostile actions in Yemen and have mobilised forces closer to the Red Sea in the face of threats of US-led strikes.

Forces loyal to Yemen's internationally recognised government said they foiled a Houthi attack on their bases in Bayhan, a district of the Shabwa province, on Wednesday.

The Houthis had tried to take positions controlled by Southern Giants Brigade, a pro-government force, near villages bordering the Marib province.

But they were pushed back the same day, according to reports from the Southern Transitional Council (STC), which backs the Giants.

The Houthis were seen mobilising in areas closer to the sea, and moving rockets, an STC representative told said, citing reports from its forces.

In December, the Houthis attacked positions in the Kirsh district of the Lahij province with drones, killing two civilians, according to STC reports.

Yet smaller escalations had occurred almost daily in the past month, the STC representative said.

It comes as western countries, led by the US and UK, issued an ultimatum to the Houthis on Wednesday, calling on the rebels to stop their attacks on shipping in the Red Sea.

The attacks on commercial shipping began in November, with the Houthis claiming they were a response to the Israeli bombardment of Gaza.

Over 20 Houthi attacks with missiles, drones, fast boats and helicopters have taken place since, prompting clashes with the US Navy.

The US and UK are probably planning to target Houthi launch sites with air strikes, military analysts said.

Yet growing hostilities within Yemen further threaten the fragile truce. The Houthis have been fighting a civil war against Yemen’s government since 2014, and now control parts of Yemen’s north and two of its ports.

A Saudi-led peace plan is nearing completion, with economic concessions expected for the cash-strapped Houthis.

The US will seek to protect the peace process in any of its responses to the Houthi attacks on the Red Sea, according to a US-based diplomatic source.

The White House earlier this week sought to distinguish Houthi threats in the Red Sea from Yemen’s civil war, of which peace prospects had been hopeful before the Israel-Gaza war.

A senior Biden administration official on Wednesday said that the civil war is “just a different issue” from Houthi escalations in the Red Sea. “This is about a threat to a major commercial shipping route, which is really distinct from the actual Yemen Civil War,” the US official said, adding that Washington is in “very close consultations” with its Gulf partners, including the Saudis.

“We do not want to see the Yemen Civil War reignite,” the official reiterated.

Other western officials hope that the talks on a framework peace plan opens up a "big role" for Saudi Arabia to exert influence on the Houthis in the current crisis. One western official said the assessment is that the Houthis are committed to the peace process and expressed hope that the group's key partners, including Iran, could start to calm things down rather than escalating the confrontations in the Red Sea.