Yemeni military says it has 'secured' Red Sea waterway
Saudi-backed forces gave conflicting reports of whether they had also seized the port city of Mokha, near the Bab al-Mandab Strait.
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 its 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 later told news agencies Reuters and AFP that the forces had only reached the city's outskirts.
The Houthis denied losing Bab al-Mandab and Mokha and said they had struck Riyadh's airport and other locations in Saudi Arabia in retaliation for the air strikes.
Saudi Arabia condemned the attacks and reiterated calls for the UN Security Council's permanent members to support Yemen's internationally-recognised government.
Turkey and Pakistan, allies of Saudi Arabia, meanwhile held an emergency meeting in Riyadh and agreed to rapidly deploy military forces to Saudi Arabia in an invocation of the Mecca Joint Defence Agreement, according to a statement shared by Pakistan's foreign ministry.
UN Secretary General Antonio Guterres condemned "the continued Houthi cross-border attacks" on Saudi Arabia and said he was "deeply concerned by the sharp escalation in fighting", in a statement to AFP.
Children brave snipers and mortars to go to school near Yemen front line
The offensive launched by the pro-government National Shield, Giants Brigades and Tihama Resistance forces in south-western Yemen on Monday reportedly saw the Houthis pushed out of most of the coastal areas they seized last month.
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 cited a Houthi military source as rejecting as "Saudi propaganda" the claims that the group had lost control of Mokha, and that the group remained in control of Dhubab, Bab al‑Mandab and the Kahboub mountains near the coast.
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.
In addition to the strikes on Riyadh's international airport, the Houthis attacked an Aramco oil refinery, and Abha airport, as well as other sites, according to Yemen's Houthi military spokesman Yahya Saree in a statement on Telegram.
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.
