Yemen's government says it has launched an offensive aimed at retaking all territory held by the Houthis

Yemeni pro-government forces backed by Saudi Arabia say they have "secured" the Bab al-Mandab Strait at the southern end of the Red Sea, at the start of a major offensive against the Iran-backed Houthi movement.

The Yemeni military also said in a statement that National Shield, Giants Brigades and Tihama Resistance forces had captured the Red Sea city of Mokha on Monday afternoon with the help of Saudi air strikes.

But in conflicting reports, unnamed Yemeni government and military sources told news agencies Reuters and AFP that the forces have only reached the city's outskirts.

There was no immediate comment from the Houthis regarding Mokha.

Four government sources told Reuters that Yemeni forces had reached the outskirts of Mokha late on Monday, and that Houthi fighters were now retreating.

Government military sources who spoke to AFP would not confirm the capture of the city, but said "our forces took control of the Dhubab military airfield and cut the road linking the Dhubab district to the Bab al-Mandab area".

Earlier, the Yemeni military also said its forces had seized Dhubab airport, 45km (27 miles) to the south, and were besieging Houthi fighters inside the nearby town.

Houthi-run media denied reports that government forces had also made advances in Dhubab.

The government said operations had also begun on other fronts on Monday, including the capital Sanaa, which fell to the Houthis at the start of the civil war 12 years ago.

Meanwhile, a Saudi-led military coalition said its fighter jets were providing "round-the-clock" air support to the pro-government forces and had destroyed 324 "high-value" targets since the start of the offensive.

Saudi air strikes killed a schoolgirl and a woman in the Sanhan and Saawan districts of Sanaa on Monday, according to Houthi-run Al Masirah TV.

Houthi spokesman Mohammed Abdul Salam said Saudi Arabia was committing "dozens of massacres" and that it must "bear all the consequences".

The Houthi-run Humanitarian Operations Co-ordination Centre warned civilian airlines that Saudi airspace, except for the skies above the Islamic holy cities of Mecca and Medina, was no longer safe because it had become "a theatre of operations".

On Sunday, the head of Yemen's internationally recognised Presidential Leadership Council announced the beginning of an offensive, dubbed Operation Yemen Dawn, aimed at retaking all territory held by the Houthis.

Rashad al-Alimi insisted that all opportunities for de-escalation had been exhausted and called on all forces to carry out their assigned missions "until the country is liberated from the grip of the Houthi terrorist militia".

It came after the Houthis reportedly cut a mountain road near the south-western city of Taiz, effectively leaving government forces and residents there surrounded.

The Houthis also said they had launched ballistic missiles and drones at oil facilities belonging to Saudi Aramco in Riyadh and the Khurais area of Saudi Arabia in retaliation for dozens of Saudi strikes on their territory.

According to BBC Verify, satellite imagery from Saturday shows thick, dark smoke coming from the site of a strike at the Aramco Riyadh Refinery, in the city's south-east.

A similar plume of smoke can be seen rising from the Khurais Central Processing Facility as well as from a potential strike point in satellite imagery from Sunday.

Yemen has been devastated by a civil war that began in 2014, when the Houthis ousted the government from Sanaa. The conflict escalated in 2015, after a Saudi-led coalition of Arab states intervened in an attempt to restore the government's rule.

A four-year-old informal ceasefire began to unravel in July, when the Houthis announced a "maritime embargo" against Saudi Arabia and began missile and drone attacks on Saudi airports, oil facilities and tankers in the Red Sea.

The Houthis said they were retaliating for a Saudi blockade of ports and airports in their territory, as well as an air strike on Sanaa airport that they blamed on the kingdom.

Last month, the Houthis launched a surprise offensive along Yemen's south-western Red Sea coast and quickly ousted pro-government forces from areas overlooking the Bab al-Mandab Strait, including Mokha, Dhubab and Perim (Mayyun) Island.

They said they posed no threat to international shipping passing through the waterway but that they would continue to target vessels from Saudi Arabia.

However, the seizure of the strait contributed to a surge in global oil prices because Saudi Arabia had been relying on the Red Sea for oil exports since the US and Israel's war with Iran effectively closed the Strait of Hormuz in the Gulf.

At least 959 people have been killed and 5,000 injured in the fighting in Yemen since 6 August, according to the government's health ministry.

The UN says another 197,000 people have been displaced.

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