More than 50 security personnel have been killed and 200 injured in a Houthi missile strike on a camp in Yemen's central province of Shabwa, local authorities say.
A spokesman for the Saudi-backed Yemeni armed forces said the Iran-backed group launched three ballistic missiles at al-Alam camp near Ataq city, which was being used as a training centre for recruits to the security forces and police.
The head of Yemen's Presidential Leadership Council, Rashad al-Alimi, condemned what he called the "criminal attack" and promised a "firm response".
The Houthis' military spokesman said they had targeted "Saudi enemy concentrations".
Yemen's devastating civil war has flared up in recent months.
At the start of October, pro-government forces launched a major offensive that aims to retake territory in western Yemen that is controlled by the Houthis.
With air support from a Saudi-led coalition of Arab states, they managed to regain control of territory on the Red Sea coast that overlooks the strategically important Bab al-Mandab Strait, which the Houthis captured in a surprise assault in September.
However, fierce fighting is continuing there, as well as around the besieged government-controlled city of Taiz, and to the north in Marib and al-Jawf provinces.
The Houthis have also responded to the Saudi air strikes by launching missiles and drones at airports, energy facilities and military bases in neighbouring Saudi Arabia.
Monday's attack in Shabwa is one of the deadliest reported since the start of the escalation.
Shabwa province's media office said in a statement that ballistic missiles struck the Martyr Ahmed al-Sulaimani Training Centre, where recruits from several provinces were undergoing training to be members of the internal security forces. According to a preliminary assessment, 53 were killed and more than 200 injured, it added.
A video posted on social media appeared to show several bodies scattered across the ground.
Shabwa's deputy governor, Fahad al-Khalifi, told AFP news agency that hospitals in the province were overwhelmed and had been forced to transfer the most seriously wounded to neighbouring Hadramout and Aden, where the government is based. Some of them were in a critical condition, he said.
Information Minister Moammar al-Eryani said the attack constituted a war crime because the internal security forces training centre was not a military target.
He also accused the Houthis of "attempting to fabricate a false media victory, boost the morale of its collapsing elements, and cover up the defeats and setbacks it is suffering across various combat axes".
The Houthis' military spokesman, Yahya Sarea, said in a statement that the missiles targeted a gathering of "Saudi enemy" forces at al-Alam camp, which he said was run by Saudi officers.
There was no immediate comment from Saudi authorities.
In a separate development, Houthi-run media reported that a Saudi air strike on a home in the Sahar district of the Houthi-controlled northern province of Saada on Sunday killed at least 10 people and injured 23 others, many of them women and children.
According to the Houthi-run health ministry in north-western Yemen, a total of 141 people had been killed in Saudi strikes over the past seven weeks.
The government's health ministry, meanwhile, said last week that at least 1,282 people had been killed in the conflict across Yemen since 6 August.
In Saudi Arabia, at least 19 people have been killed in Houthi attacks targeting the kingdom's airports since the beginning of October.
Yemen has been devastated by a civil war that began in 2014, when the Houthis ousted the government from the capital, Sanaa. The conflict escalated in 2015, after the Saudi-led coalition 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 what they call a Saudi blockade of their territory, as well as an air strike on Sanaa airport that they blamed on the kingdom.