After the UAE claimed that 22 of its troops were killed in Yemen and Bahrain, it lost five more soldiers on Friday, which proved to be the deadliest day for a Saudi-led coalition battling Yemeni Shiite rebels.
The Yemeni government said an "accidential explosion" at an arms depot at a military base in the eastern province of Marib killed the 22 Emiratis, but the rebels said their fighters launched a rocket attack that caused the blast.
Coalition ally Bahrain said five of its soldiers were killed in southern Saudi Arabia where they had been posted to help defend the border with war-wracked Yemen, but it gave no details.
The Arab coalition led by Riyadh has since March battled Iran-backed Huthi rebels to restore the rule of President Abedrabbo Mansour Hadi, exiled in Riyadh.
Around 60 people, mainly military personnel, have died in cross-border rebel attacks in the south of the Saudi kingdom since the coalition launched air strikes on the Huthis and their allies.
The campaign was launched as the Huthis advanced on the southern port city of Aden, after having taken control of the capital Sanaa without resistance in September 2014.
The United Arab Emirates armed forces, in a statement carried by state news agency WAM, did not disclose the circumstances of what was its highest casualty toll of the six-month-old air war.
The Emirati army had previously announced at least eight deaths in Yemen among its ranks.
A total of 33 Yemeni soldiers and coalition forces were killed and dozens of people were wounded in the blast at the base in Safer, 250km (150 miles) from Sanaa, the pro-Hadi army command said.
A thick plume of black smoke was seen billowing from the base several hours later.
Friday's heavy losses for the coalition came as Saudi King Salman was in Washington for talks with US President Barack Obama at which Yemen figured high on the agenda.
More than 4,500 people have been killed in Yemen's conflict, including hundreds of children, according to figures from the United Nations, which has warned that the impoverished country is on the brink of famine.
According to military sources, the coalition sent reinforcements to the Safer base this week, including tanks, armoured vehicles, troop carriers, rocket launchers and Apache helicopters.
The extra military hardware as well as troop reinforcements aim to boost "the counter-offensive launched by loyalist forces and the coalition to advance on Sanaa", one military official in Yemen said, asking not to be named.
The Huthis, meanwhile, said their forces had killed "dozens of officers and soldiers of the mercenaries in the Saudi aggression" when they fired a Tochka ballistic missile at the Safer camp.
The strike was "revenge for the crimes and the war of extermination being carried out by the Saudi aggressor and its mercenaries", they said. The Yemeni government denied the Huthis' account, saying the explosion near an Emirati encampment in Safer was caused by "badly stored munitions".
An initial investigation, however, found that the blast was triggered by a surface-to-surface missile fired by the rebels, one Yemeni military source told AFP.
The Huthis, who advanced from Sanaa to overrun large chunks of the country, were driven out of the southern port city of Aden in July. They have since been on the defensive in southern Yemen, losing control of several provinces.
The Arab coalition has also sent in troops, with Saudi media reporting that roughly 1,500 soldiers, most from the UAE, had entered Aden. The UAE only confirmed last month that its troops were on the ground there.
The blast in Safer came as loyalist forces kept up their drive to claw back territory lost to the Huthis over the past year.
Coalition warplanes later on Friday carried out air strikes on the rebel-held defence ministry complex in Sanaa and also targeted arms depots in the north of the capital, witnesses said.