ABU DHABI: An arms depot explosion in Yemen killed 22 soldiers from the United Arab Emirates, in the country's heaviest loss since joining an Arab coalition battling rebels, military sources said on Friday.

The two sides gave conflicting accounts of the cause, with the Houthi rebels saying they carried out a rocket attack and Yemeni military sources describing it as an “accidental explosion”.

The UAE is a key partner in the Saudi-led coalition that launched air strikes against advancing Iran-backed Houthi rebels in March after they forced President Abedrabbo Mansour Hadi to flee to Riyadh.

More than 4,500 people have died in the fighting, including hundreds of children, according to UN figures.

The UAE, a longtime Western ally, did not disclose the exact circumstances of its own highest casualty toll from a single incident in the six-month-old operation.

The Emirati army had previously announced at least eight deaths in Yemen among its ranks.

The arms depot blast at a military base in Safer in oil-rich Marib province, 250 kilometres east of the capital Sanaa, also killed several Yemenis, a source at the scene said.

A thick plume of black smoke was seen billowing from the base several hours later.

According to military sources, the coalition dispatched reinforcements to the 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 Houthis, for their part, 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 a camp in Safer.

The attack sparked fires in arms stores, damaged Apaches and destroyed Emirati armoured vehicles, they said in a statement carried by the Houthi-controlled Saba news agency.

It said the strike was “revenge for the crimes and the war of extermination being carried out by the Saudi aggressor and its mercenaries against the Yemeni people”.

The Yemeni government denied the Houthis' account, saying the explosion near an Emirati encampment in Safer was an accident caused by “badly stored munitions” and that a probe was under way.

An initial investigation, however, found that the blast was triggered by a surface-to-surface missile fired by the rebels, a Yemeni military source told AFP.

Apache strikes

The Houthis, who had seized the capital Sanaa in September 2014 before taking over large chucks of the country, were driven out of the southern city of Aden in July.

Read more: Pro-govt forces retake Aden palace, coalition reopens airport

They have since been on the defensive in southern Yemen, losing control of several provinces.

The Arab coalition has also backed the loyalists with military equipment as well as 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 in Yemen.

The deadly 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.

Interior Minister Abdo al-Houzaifi told AFP that on Thursday night pro-Hadi forces armed with “sophisticated military equipment and backed by Apaches bombarded rebel positions in the south and centre of Marib province where the Houthis have pockets of resistance”.